In terms of motor swap, it really depends.
A good starter would be to buy one with a L28 motor. This motor allows a lot of flexibility in tuning. You can keep the EFI if you want to keep reliability etc., but I'd swap some early Z SU carbs (ztherapy.com), to get that old skool feel. If you want to put that $10k towards motor work, get some triple carbs (weber, solex, mikuni). All are a good choice.
If you want to stay EFI, you can swap a L28ET motor (from the 280ZX turbo). That'll get you major power in a early Z.
Seeing as you're just getting your license, I'm assuming you're on the young side. I suggest you stay with the stock motor to learn how much power you can handle. That's the first step in not becoming the infamous "young kid that posts about wrecking his/her car" thread.
Learn your strengths and weakness, tweak the suspension for more power in the future.
Enjoy your future Z!!