Heyo,
I want to buy a small (500 point-ish) tyranid army for my boyfriend for his birthday. I recently started
40k and am still rather green, so I am not sure what the best option is. He has never played before, he likes space hulk ( specifically genestealers ), and I am trying to convince him to try out
40k with me.

What do you think the best option is? Should I buy him a battle force? Or would it be better to buy him a couple of boxes of core units. And what are good core units to buy him for Tyranids if that is the case?
Thanks for any help, and sorry if this is the wrong place for this question.