1) how can I make in sync
Sync shouldn’t be an issue since you’d be using one GPU
4) none of them have SDI ( it’s a low budget project)
The big limitation of SDI is that you can’t do 1280x800 or 1920x1200.
5) if I consider to buy the Optoma or EIKI they have HDBaseT I need some senders can you recommend any brand! I did buy with Oaktowm advice some very reliable Atlona 70ps but the sender only it’s $300 instead of $350 for the kit. I’d love to put one unit in rack with media server i7 4.0ghz 32gb ram and 256 ssd for Windows 10 and 960 ssd for the content and Asus strix gtx 1080Ti.
Atlona AT-HDTX, I just bought 5 for a new project on Amazon and they are ~$180 a piece.