There is no issue getting it across the line for restoration- just patience. Not that big of a deal.

The company you got a quote from would probably not be doing the blasting- "They" would farm it out -shuttle it to and from and pay for it then you would reimburse them as part of the bill.. As far as the sand blasting etc- yes the person who did mine can work all of that for much less than you were quoted. Mine was taken all the way down to bare metal- and every nut and bolt removed and re-done- total resto from ground up excluding the motor- it was already done at some point, so we just checked a few things on it. He can rebuild the motor as well however if needed.
As far as the door panels- it is hard to find repops that fit really well- some folks have brands they prefer- I would ask around. If the originals are in good shape I would try a really good cleaning before throwing them away. Personally I would not get them sprayed- i would replace them if they are truly worn out.
I would start by ordering the PHS document for your car- it will tell you exactly what it is supposed to have on it. It can answer your antenna question as well. The Bible for your car basically.

You should decide if you want to go original or resto- mod or somewhere in between. Only my opinion- but if you have the original motor in that HO I would stay original with the rest of the car.

There are many tricks for these cars, and things that you can do to improve performance and ride. I would ultimately take it to someone who knows these Firebirds instead of a normal resto- shop who may have not done one before. They will know what parts are missing and be aware of part resources and do a much better job in the long run.

Any questions you have as you progress can be asked on this website- they are LOTS of folks who have real in depth knowledge of these cars.