Here's a post with my
current setup. The day that I posted that, I had planned on migrating my user data to the 'data' partitions, but currently it's just photography stuff.
That should tell you a lot about how I partitioned everything. The few times I've changed disk setups, a spare SATA drive or two has let me do it without too much fuss - clone partitions off disk to be re-purposed, check data, erase first disk, rinse, repeat.
I have a SeriTek four-port eSATA card. I have no complaints with it. I had a SeriTek two-bay enclosure, but it died after a power outage (yes, I have a UPS, yes it was on it, no, I don't know why - one too many power bumps, I guess). I replaced it with two Vantec eSATA/USB enclosures like the one I already had for TimeMachine.