Well that is quite the pickle that you find yourself in there: a more experienced player, with a newer codex!
But do not fret, brave Shas'el! You are a Tau player, a servant of the Greater Good. And that means that you have something that your opponent does not... HEART.
The battle you face will be difficult, but it will be a Trial by Fire, and it will not be your last. If you claim victory you will stand in victorious glory with your new-found skills... and yet if you lose... if the flesh should be singed and scorched from your body, then the medi-drones will replace it, and it will be stronger... and lemon scented!
While people might look down on our dusty codex, it still strikes fear into their hearts out of the corner of their eye. There is a collective cultural memory of the hay-day of the Tau. They remember when the wounds we caused were fresh, when our weapons were shiny, and when their most precious of units fell to our devastating firepower. While those days might be on hiatus for the moment, pieces remain. And they can be a tool in your psychological warfare.
The Mighty Railgun
It's name is synonymous with destruction. Your heavy support choices have a strong foundation, but you must be careful to use them to intimidate just as much as destroy (as well as to "pull" the army).
Your hammerhead looks pretty solid, keep it moving for those cover saves! And this is a good place to drop a few extra points if you still have some later (decoy launchers/flachette discharger/sensor spines).
For your broadsides you might consider splitting them up. Personally, I agree with the earlier sentiment that mobility will more likely help you out (as much as I do love some BS4). I would recommend the Advanced Stabilization System, and upgrading to twin-linked plasma rifles, with a hard-wired multi-tracker. This is a useful loadout with multiple mobile shots that will SCARE people. Not to mention that the upgrade to character means that your broadside now has Precision Shots (even scarier!). This is also a GREAT place for extra points in the form of shield drones. Broadsides are one of the Top 3 best places to put shield drones in the entire army.
So far, this gives you the ability to create two fire bases (one Broadside each) with a third option to move between the two or flank (Hammerhead).
As far as your suits go, that is the most complicated part of any Tau army. Crisis suits are supposed to be the workhorse of our cadres, but they aren't quite as "heavy" as they once were. While I think flamers make great back-up weapons, I would probably advise against them for this list. Specifically because you have other options at your disposal. As was mentioned, the Submunition round is a great attack, and I think that points might be better spent adding an Airbursting Fragmentation Projector to your list instead of flamer suits. The AFP is additionally a point of fear in the memories of many players, because it is unique in our army (not necessarily other armies) and tends to be associated with high-ranking characters. My suggestion would be Twin-Linked Missile Pod and AFP on your Shas'el. No need for Multi-Tracker if it helps with points.
I would also tend to recomend a few fusion blasters (don't need to try and spam them, but two or three would be nice). Especially against necrons, who could completely surprise you and show up with a Monolith (or two if he's a jerk lol). Even against just regular vehicles the Quantum shielding can be annoying to break through. Fireforge+ suits might be the way to for a deepstriking squad: Twin-Linked Fusion balster and Flamer. The poor man's close ranged Fireknife's slightly uglier cousin, as it were
The idea being that a mid-to-low priced unit of these gives you versatility at the behest of range. But don't forget that crisis suits are faster now. You can forgo a round of shooting to move 6+3d6 inches to get into place. And DO NOT forget that your range means much less when your enemy flies at your face at full speed. The flamers ignore your low BS for CHEAP, and they are very useful for their wall of death ability during overwatch (much more efficient damage vs. the unit attacking you), in addition to the aforementioned scarab stomping power! Now the fusion blaster offers some nasty anti-tank as well as anti-monstrous creature dakka (for instance against tomb spiders, that you know... spit out scarab swarms!
). They are also "intimidating" in a familiar sense. When you tell someone that you have two twin-linked melta-guns that can Jetpack around... they start thinking twice about their movement choices and target priority.
I don't mean to inundate you with too much information, but I hope this is helpful, at the very least from the "psychological" stand point. I never really like math-hammer all that much (only considering statistics), seemed too separated from the human element, you know?
With your most recent changes to the list, it might be interesting to throw the AFP onto your XV-81 Shaso, for a WHOLE LOT of line-of-sight ignoring, cover save evading dakka
On an even more personal note (and to be entirely honest, I just don't like Fireknives, I never have. Maybe it's a "tau hipster" moment for me, because everybody else loves them, but their just not for me, at least in this codex... crosses fingers
) I must take a moment to spell out the wonderful benefits of the missile pod in this scenario. The humble missile pod is a very versatile weapon, indeed I believe it to be the hands down single best weapon on a Crisis suit. For your scenario, it has a high strength value (wounding on 2+ even against their tough elites choices and bikes). It has the longest range (three feet is nothing to scoff at, especially on a mobile platform). It has two shots (always a plus), at full range (double plus!). It will cut through necron warriors, flayed ones, scarab swarms (with instant death!), and bikes like a force sword through butter. Deathrains are a beautiful, and simple crisis suit, and would be completely welcome in your anti-necron-invasion force. They can shoot at fliers reasonably well, even glance almost every vehicle they have (and certainly take them down after the quatum shields have dropped). Their mid-range AP actually makes them a great choice against certain heavy armor units like Dispersion Shields or Wraiths with their invulnerable saves (you aren't "wasting" your AP, so to speak). An XV81 commander with two teams of two Death rains (Twin-Linked Missile Pod with Targeting array) would be a reasonable choice considering your other units (namely, three railguns), especially at 1000 points when markerlights are scarce or in this case non-existent.
Additionally, your tactics against necrons (and in general) would usually be better suited to be more like "the shell game" than a "turtle". By that I mean, castling up is usually a bad idea these days, especially against an army that can out-shoot AND out assault you (not that it's too hard these days lol). By "the shell game" I mean shuffling your units around, stay moving... always moving. It DOES NOT have to be in reverse. Sometimes moving sideways is a great way to "get away" or even to just distract. Move left for one turn, let him Zoom over to catch you, and then swerve right back to where you came from. Your opponent will start to feel "tired" of moving units like fliers around the board without actually using them to do anything.
As far as adding another unit, I would say push points towards your troops. Splitting the units up into groups of 8 isn't half bad. Makes it harder to kill them all in one go (theoretically lol) and lets you shoot at different targets. I would say either run a devilfish for one unit (in reserve, air cavalry style), or take the kroot. These days kroot aren't so good, but they will actually do alright against most necrons in combat because of initative. Once again, this unit is for scoring, not for killing, so don't get carried away. Outflanking with them is a good choice to keep them safe for a few turns, sneak onto the board past the enemy near their board edge and snag an objective (preferably in a forest
Finally, as always, don't get caught up in the arms race too much. Kill your opponents troops. Kill them fast and kill them HARD! Do what you can to protect yours, as the vast
majority of games in 6th edition are objectives based.
So in summation, Intimidation (with big guns), Relocation (with constant mobility), and Devastation (directed at his vulnerable and vital scoring units).
I can only hope that the quality of this post has matched it's quantity, and most importantly, that you have found it to be useful.