Yep, s'about right. BB Combo > SP Combo is the basic thing to do. The only thing that really changes once you get SE combo is you go SP > SE when you're off-tanking or when you've got enough of a threat lead that you don't need BB mixed in.

For cooldowns, sure. You're not at a point where you need a huge amount of strategy with them, but you've got the general idea. You can either rotate through the small ones to keep your average mitigation a little higher, or combine them to make them a bit more worthwhile. Either way, you save the big ones for big hits. A lot of people pair Conv and ToB together, since Conv helps get the extra HP of ToB filled back up. You can use ToB (to a degree) either reactively or proactively; if you use it right before a big hit you know is coming, it's basically like absorbing part of the hit with the extra HP.

Anyway. You're doing fine. You'll figure the fiddlier stuff out when you need to.