Sorry man I thought you were experienced in this already.
To the block and fittings, brand is completely up to you. I personally use Bitspower fittings because they have a lot to choose from. Since you have a small case I feel you should use 3/8th tubing with the usual 1/4" thread fittings. I also like EK blocks, again just a personal preference but that Swiftech block is nice and adds a bit of bling to the mix. Basically they all perform to some degree about the same. Make sure to get your metal mixture correct though. Don't mix copper with nickel ect.
For your application I would use a combination of angle and stubby fittings and although they are more expensive you might want to consider compression fittings to get more umph from the pump on the block. Going by what others have said it should handle 2 blocks and rads ok, but in this case too much isn't a bad thing. Bitspower also has different colors to chose from if that's your thing.
For your block selection, I would look at something that has the vertical fitting placements so your fittings are on the back of the card facing the CPU. Use straight stubby here on the GPU. CPU going to right side of block, output of GPU going towards top rad, top rad rear fitting going towards front rad, front rad back to CPU (or to res, then back to CPU). You will probably have to use angle fittings on the top rad.
An optional setup would be same CPU/GPU setup, but right side GPU going to front rad, rear output on front rad to top rad, top rad to CPU. Input res if using one.
For tubing, I personally use tube I bought from Lowes, but in your case I would go with something like this.
PrimoFlex Advanced LRT Tubing - 3/8in. ID X 1/2in. OD - Onyx Black Products Model: PFLEXA-12-BK [PFLEXA-12-BK] : Performance-PCs.com, ... sleeve it and they will come
Now if you're up for a bit of Google and a LOT of patience and practice to get a great setup, rigid tubing is the new thing. My next loop will be rigid tubing because it just looks fantastic.