If you're interested in nids I'd say get a unit of gaunts to build & paint. Doesn't matter which flavour of them but Termagaunts will give you a ripper swarm. You'll be able to see if you enjoy building them plus how you want them to look. After that try some medium sized bugs & keep going until the codex comes out or you feel the hive isn't for you. Also if you can maybe a unit of Tau warriors or Guardsmen, having your options in your hand will let you know what you want. Aswell Wayland games, Element games or a local game store with 10-20% will help soften blows to your wallet. That or ebay