I just tried out my 1-point uber smiter. I'm using some fairly standard gear, but found I ran out of mana pretty easily.
My current setup:
Helm: Guillamune's (thinking of socketing with Ber or Um)
Armor: Treachery (will upgrade to Fortitude soon and just use this to pre-buff)
Boots: Gore Rider's
Ring #1: Ravenfrost
Ring #2: Resists
Charms: Life & Resists
Is there something people usually do to keep their mana up? Where should I be getting my mana leech from? Should I be aiming to get a mana leech ring?
A Call to Arms on your switch helps. Also, Mana Leech (and Life Leech) don't work with Smite. Personally I've never had a problem with mana as a smiter, even with really poo gear. I'd just carry mana pots with a few full rejuves (one column of rejuves, three columns of Super Mana pots) and simply restock after each Uber kill.
If you currently do not have a CTA you could buy a wand with Life Tap charges (you can get over 100 charges on a wand) and simply cast Life Tap yourself before engaging with an Uber, saving you a need to heal at all and allowing you to stock 16 mana pots.
If all else fails, get yourself a Mana Leech ring and switch over to Zeal as needed.
One option is to socket for damage taken goes to mana (ith rune or better yet jewel with that and other good mods) but even if you don't, so long as you're pulling the ubers separately (IE you don't have baal on you while you're trying to kill meph) it shouldn't be a big problem.
I roll with 3 lines of juvs and one line of mana potions in my belt. I never need mana potions on meph or diablo, just because the mana cost of smite is so low. Against baal I use my line of mana pots.