I was wondering if anyone had any experience with this or any advice. I've spent too much money to back down now, so please don't just say get a cage off of ebay.

I know finches are very sensitive to smells, and my first question is about the interior of the cabinet. I just realized that it is painted on the inside. Will this affect the birds in any way?
Next, there are some old hutch lights near the top. I was going to try to replace the bulbs with full spectrum light ones, but looking online I keep seeing that people have the lights on the outside of the cage. Can I have lighting on the inside, or is there harm to the birds in this? Should I just remove lighting all together?
I am planning to keep the glass in most of the door except one, will this be enough ventillation? I am extra worried about this because of the painted interior, and I keep going back to the cabinet and sticking my head inside to see if I can smell any paint.

Also, I will be replacing the glass on the door with either a small type of chicken wire or metal grate. Does the type of metal matter, and can I paint it to match the cabinet? I know I have to find child safe paint, I just want to make sure that finches are not chewing birds like parrots.
I have purchased some manzenita perches and hanging feeders for the interior. Do finches like toys? Would they like mirrors or swings like other birds? My husband grew up with Cockatiels and Parakeets so he is not sure on this point either. So far they seem to just like to sit there and chirp at each other.

Lastly, The dimensions of the eventual cage will be 50" by 50" by 15" wide, and we have two finches. I'm assuming this will be large enough if we expanded our population, but I was wondering if there was such a thing as too large of a cage? I know there are certain rules (like no round tops), so I didn't know if there was one about cage size.
Thank you so much for your help! I've taken on a pretty big project I think...