Those B&M are ok , I have used them but if using the Dacron type they need changing regularly. You can get a gauze type also , they are a torqueflite part.
Or you could use a C6 4x4 filter with he rubber grommet and make up an extension tube. I'll see if i can add a pic of one I did.
That large cooler is certainly not excessive IMO.
The R servo certainly isn't necessary , there are good factory servo's also that will do you well. If you are building the trans look at the Alto 2.5" wide band is a nice addition.
Servo lever also can be changed but that will depend on the servo you have .
Theshift kit is a definite. A stock C6 shifts way too soft. The Transgo SK-6 kit does well . It gives a nice crisper shift without being harsh. They give a choice of 3 springs for the accumulator , i like the setup with a single spring for the shortest shift .
Type F fluid = YES
I've not used the different ratio kits . Some guys say they are good .. Not too sure myself. The factory gearsets will give you good service if in good condition
What I would look at for towing is to make sure you get 5 clutches in each pack. A stock top gear only has 3. There are companies that sell a drum ready to go like Broader performance or you can machine yours