Though if you are making a fully custom loop (not a kit like I did), I advise getting a dedicated pump and reservoir. Iv found that having a pump/res makes bleeding and filling somewhat difficult. Also having it mounted in the 5.25" bays makes it fairly loud since you cant really pad it to reduce vibrations.
Would depend on the particular radiator, fans and whether you are running in push/pull.
At a rough guess, maybe. A single 360mm could hold it, but you would be at the threshold I think.
Might take two or three reads to fully understand, but it covers pretty much everything.