I like your train of thought to start with a BB 55. It's better to crawl before your try to run. Your plan of going to the bigger tank later also sounds reasonable to me.
RO - generally it's COMPLETELY unnecessary unless your breeding discus, and not always even then. I'd save your money and not bother upgrading your Coralife. If you ever end up with a pair and want to set up a 20 or 29 as a breeding tank the Coralife would still handle that. Of course it usually doesn't stop at one added breeding tank and you might have to upgrade later, but that could be a couple years down the road if you even want to take that path. It's not for everyone.
I personally use Brute Rubbermaids for my aging barrels and have no problem recommending them. There are lots of other good options as well, but they work. I keep a lid on mine more to keep the heat in than anything, but I think that's pretty optional. I don't have any holes in my lids, they don't seem to fit that tight, but I doubt it would hurt either.
As far as pumps go I use Mag Drive MD-7. My runs are about the same as yours and it fills or empties at a pretty decent rate.
Good luck and enjoy.