Welcome! I use to be a sneaker head as well, but it was a costly hobby so I stopped. That's nice that you can use some of the money from selling them towards your Z.
Now, for the Z you are looking at you can probably get 1-2k off the OTD price depending on how good of a negotiator you are. I got my 2011 for 36OTD but mines an auto, base. So your price, considering its a manual I think is good.
The prices you see on edmunds, true car and etc are usually invoice or list prices, the only way to know what you are truly going to pay when you drive your Z off the lot is going by the dealer quote. It seems you've gotten one now, (34,330) work on negotiating the price a little bit it may be hard as the 2012's just came out, but as the winter approaches, dealers may be willing to give larger discounts, aim for the 32-33k OTD range, that would be a solid deal for a new 2012 base in my eyes.
Good luck
