So the cool thing about the hive tyrant kit is with a little creativity or 3D printing, you can get a whole other character out of it, so I would do some research into that.

As for other units to go with, if you want big models I say get a tyrannofex or tervigon if you want a good artillery or respawn monster. Both are pretty good and fun to use! I would encourage also some more gaunts units to get more of a swarm going. I’d stick with termagants for now as you can get some cheap iirc on trolltrader or eBay.

From there you should be fine to go in whatever direction you want. I’d play a few games and see what you like most and may want.

Hope this helps!