I would personally go for missile pods on all 3 of your crisis suits, you want as much range as you can against tyranids. Split your pathfinders into 2 units of 5.
If you just have the get started! box and pathfinders, the only way you can field the list is if you run it as a CAD (or unbound).
Use the ethereal as your HQ, 2 units of 5 fire warriors as your troop choices (1 with SMS DS8 turret), 3 crisis suits and then 2 units of 5 pathfinders as fast attack
Those are my recommendations. As others have mentioned, tyranids are fairly low tier at the moment so you should be ok. The best thing to do if you're playing casual with friends is to try stuff out and figure out which units you enjoy playing and like the look of.
There's loads of really friendly experienced players on the forum here, so just ask anything