How to stream video (and process) into FPGA

1. GigE Vision is a UDP Packet based interface. So you will need to cope with the decapsulation to get the data out of the UDP packets. Something like DVI or Cameralink just gives you pixels directly on the bus with sideband sync signals, and so is much easier to handle. Note: I have never used GigE Vision. But from reading around it is not an open standard, and so you may have to pay fees. You can submit a request for the standard here: https://www.visiononline.org/form.cfm?form_id=701

3. Its not that high. The pixel rate is lower than FullHD (1080p) so should be perfectly possible

Bottlenecks are likely to occur in the interfaces - usually the memory.

I am rather skeptical about making your own board getting the layout and masks for your own PCB will be thousands (or tens of thousands) of dollars. The Schematic tools are not cheap and layout even more expensive (plus the hourly rate of someone to do the layout as you will need someone with good skills with the high speed tracks). And then the board itself will be multi-layered and cost a lot to manufacture.

If this is a hobby, stick with a dev board! if you were planning on selling this, I doubt you would be posting here.