I really like it when builders take the time and money to do rigid tubing. The build looks nice. I will say I am not huge fan of the purple and green but colors are a personal thing so it's no biggie. All in all a nice job.
Demci- Flex filters are the ones gsx1300rk6 is thinking of. They make a nice magnetic set for the 750D. I ended up using a screen from my old C70 but I will be getting the Demci-Flex set soon as the top screen gets messed up from the radiator screw heads. Corsair didn't think that out to well I'm afraid.I would use all of these but for the front because I have the new vented front with a built in filter.
That is much better. You are limited but not having a modular PSU and there are tricks like hiding smaller cable under the motherboard but that is still a big improvement.Edit: Also I would run the extra cables behind the mobo tray and zip tie them so you can still have the back on without having to cram it. Cable management takes time and planning and it is personal thing, how much time and care you choose to take is up to you.
Since you have so much room it's a good time to learn cable management. If you would like to learn some tricks let me know. Of course cable length can have an effect on where you run cables but I think we can do better than that. It is a good start for a rig though.
Depending on the motherboard you can fit up too a 60mm rad on top, I have only seen one that fit without an offset and that was by Tiny Tom Logan. I have a 45mm with a Z97 and it looks to have about 10mm clearance. The best fit if your looking to get the max thickness is 56mm. I know at least one manufacturer makes a 360mm x 56mm.I don't think 3 x 120mm in the front is possible.