I just picked up 4E and I've never played Shadowrun before, and neither have any of my players. I was wondering what exactly happens to a technomancer or a hacker when they go full into the Matrix. Does their physical body sort of just stand there, or can they do stuff in the Matrix while walking around in the physical world as well? Also, any tips for a new GM would be appreciated; the character creation has been really complex/a headache (coming from D&D and White Wolf games).

AR is no problem, you can do your hacking as an overlay to the real world, and still function.

If you go into full VR, you better be sitting down, because your body is about to become a ragdoll.

What are the benefits of going full VR? Better stats, more dice, I'm guessing?

Usually more passes and better stats (but not always), and you also receive +2 Dice for Hot SIM... however, VR has its own drawbacks as well, that most AR users will never have to worry about... Lethal Feedback is a bitch......

Is it true that if a Technomancers wants to hack something they have to be in full VR or do they get Hotsimmed bonuses and drawbacks while in VR...

No. Technomancers are just as capable of emulating AR with their magical radio brains as they are VR. However, this does not mitigate the fact that they have no Matrix condition monitors, so unlike how it is for normal hackers, AR really isn't any safer for their neurons.