To follow from Mij'aan's post, I think we don't really have enough information to go off, especially since you're looking to use the entirety of your collection and thus any sweeping/dramatic changes are unlikely to be realistic.
That said, I could probably lend some insight. As I've stated numerous times on this site, I do not and have never played Tau. However, I've been playing chaos for over 12 years, and my opinion on the current state of the army at 750 points is the best way to play involves a heavy infantry core. Unlike at 1500 points, I think at 750 the troop choices for chaos need to be larger and more resilient, rather than numerous, and are often well protected using things like fearlessness, ablative wounds, or squad-level buffs to whatever they're trying to accomplish. Against Tau, close combat buffs may in fact be a waste of points, but I would almost exclusively run a dark apostle at this point level.
With that said, I would make sure you have the ability to outshoot a squad of obliterators, expect (in the worst case) 25-30 scoring power armour models, potentially with fear as the crimson slaughter codex REALLY excels over the original csm 'dex at this point level, and you should definitely consider the possibility of a drake.
At 750 I would consider NOT playing a drake, but would definitely look at a quadgun instead, and that's almost the points it would take for a baleflamer platform anyway, and I would expect your opponent to consider it. Moreover, the strength of chaplain-bolstered marine squads at this point level screams for some ap3. Dreadnaughts or some kind of av13 might be a decent alternative, and I wouldn't rule out the possibility of a vindicator or even two if he knew you were going to be playing crisis suits. With all that said, I think running broadsides and plasma rifles prepares your list for most of what someone might throw at you minus the drake or an oddball typhus zombie list, so you may just want to start considering how you optimize your play. The biggest weakness of marine squads are their vulnerability to weight of fire, at least at 750, and fearless only mitigates that so far. On the other hand, cultists are really rather worthless when unsupported, and are unlikely to be ignored with so few targets on the board, rendering them pretty wasteful of 1/15 th of the chaos list per squad. Definitely plan on decimating his troop choices if at all possible, and beware multicharges from a unit of 1-2 ICs and their squad all breaking apart when they're close.
Hope it helps, and try getting some more information out for us!