I posted in your build thread. As you're a carpenter, you should build your own screen, seeing as it's a dedicated room. That's some money saved to put towards kit. As Dante alludes to, you want a good balance to the speakers and amp selection. It's a long room so absolutely primed for a 7.1.2 atmos system (3 at the front, 2 sides, 2 rears and 2 ceiling speakers)
You would need a 9 channel amp though and they are expensive. Plus 9 speakers.
I don't know how much budget you can stretch to and I know what it's like to want something installed straight away.
Your room has great potential so it would be a shame not make it sonically amazing.
If it was me, I would build my own screen, buy a really cheap surround system of eBay or something which means at least you have something to listen to....and then get saving for a full 9 channel (or even 11 channel) sound system. All depends on how far you want to go with the room.