Every smiter uses the same basic skills you listed, and what you want to spend the rest on depends largely on your own preference
Here are some options:
Zeal: I'd put 4 points in here for leveling purposes. Smite is a very tedious skill to kill large monster groups with.
Defiance: Useful for the synergy with Holy Shield, but only works if you spend lots of strength to wear high def armours, and is quite useless in Uber Tristram.
Resist Fire/Lightning/Cold: 10 points in one of these will give you another 5% maximum resistances for that respective element. Lightning is probably the most important of these, followed by fire and then cold.
There are three ways to tackle Mephisto's Conviction aura with a solo paladin:
Salvation: needs less points, ~10 combined with some resistance gear should be enough to handle the -125% resists Meph slaps you with.
Conviction: needs more points because you need at least a level 21 conviction before it cancels Meph's one, but when you get there, Mephs aura will have no effect at all on you. And if you run it while leveling sorcs will love you
Extremely high resists from equipment: hard, but doable with the right gear combo. You'll need at least 300% resists from equipment. The easiest way to do this is to use one or two items with very high resists, use them against Meph, and swap them for more combat orientated stuff against Baal and Diablo. Some things that might be useful:
-Kira's Guardian
-Smoke or Gloom runeword armour
-Sanctuary in an elite paladin shield with 40+ resistances
-4 Pdiamonds in a 40+ resist elite shield when you're really poor
Some other equipment suggestions:
-You really need something with CtC lifetap, since standard leech doesn't work with Smite. The most useful source for this is probably Dracul's Grasp, a fantastic pair of gloves which also give Open Wounds (required to stop the Ubers from regeneration, Prevent Monster Heal doesn't work on them). Another option is keeping a wand with life tap charges on your weapon switch.
-If you can't get Draculs, you'll need another source of Open Wounds, like a crafted Blood belt or Gore Riders.
-Crushing Blow is the easiest way to take down the trio quickly. Try to aim for ~70%, easily gained from Guillaumes Face (35%), Gore Riders (15%, and OW), Goblin Toes (25%, but no Faster R/W), and a multitude of weapons like Kingslayer, Fleshripper, Astreon's Iron Ward, Stormlash, ... Of these, Astreons and Fleshripper have some nice bonuses that make them stand out from the rest: Astreons has + X damage which is the only damage mod except off-weapon % ED that adds to Smite, useful in PvM. They both have nice base speed (with level 20 fana, Fleshripper needs only 20 extra IAS to reach 6 frame Smite. Astreons needs 25%) and lots of Crushing Blow. Also nice is the Slows Target mod on these weapons, which will make it less likely that the Ubers will use their special abilities against you (eg elemental attacks). In the end, Astreons clearly wins despite it's slower speed, because it has more CB, higher Slows Target, and gives a nice boost to HS and Smite.
-Gear with +max resists. I'd advise at least 85% resist fire/cold/lightning. The best source of this is Guardian Angel, which also gives a nice skill and blocking boost. Every 2 points in one of the Resist auras will also give you 1% Max Resists.
-A very nice way to get some resists is the Fade proc on the Treachery runeword armour. Equip this, go stand in a fire and when the Fade triggers you get 60% resist all and 15% damage reduction for 288 seconds, more than enough to make a nice stroll through Tristram
For strategy tips, I redirect you to the Poorman's guide I linked to in the Smiterdin topic
"We are at a very serious moment dealing with very serious issues and we are not focusing on the name you give to potatoes" - Nathalie Loisau
