1) I assume human is the current best overall race for a paladin due to the changes in racial enhancements. Now that humans get healing amp boosts and massive bonuses to multiple stats from action boosts from their enhancement trees, they seem like the only viable option. Is there anything else that could feasibly work with a first life, 28-pt. build for the type of character I'm looking for?
Paladins as a rule are feat starved, and equally (but less importantly) skill starved. So humans are nice for the bonus feat and extra skill point. A drow makes a pretty nice TWF paladin, since they get bonuses to both dex and cha, which TWF paladins need. Bladeforged are of course excellent paladins, but Bladeforged are excellent melee, period, by virtue of their innate self-healing. (Reconstruct SLA.)
2) Silver Flame or Sovereign Host? I don't know which would confer better bonuses for someone who doesn't know what to expect later in the game. In either case, the favored weapon bonuses are absolutely worthless to me since I'll be using two-handers.
Sovereign Host, without question. Unyielding Sovereignty is an excellent ability, and is the only way to remove death penalties outside of shrining or waiting. Exorcism of the Silver Flame is much less useful.
3) What does Religious Lore do? I figure it's probably in the game to mimic the "knowledge (religion)" skill from the pen and paper version, and you get it for free anyway, but do the lore feats have any practical value in DDO?
Religious Lore does nothing. It's one of many half-finished systems that never went anywhere.
4) Turn Undead on its own seems moderately useful, but is it worth speccing into Divine Light to make it do outright damage instead? Should I bother with Improved Turning?
Turn Undead on a paladin is pretty much useless outside of powering Divine Might, which is a great feature of paladins. Save your turns for divine might, and don't invest any AP into buffing your turns. (The ones to increase the number of turns are worth considering, though.)
5) Temporary hit points. As best as I can understand it, temporary hit points give you a straight bonus to HP that don't really count towards your total, but rather act as a buffer for incoming damage. Instead of reactive support (healing), they're proactive support (lets you prepare for a situation by allowing you to take an extra hit or so). How useful are temporary hit points, and is a paladin expected to buff his allies with temporary hit points all the time? Are most temporary hit points (or spell points for that matter) on a timer or do they generally stick with you throughout a quest until you get hit and lose the buffer?
Temporary hit points are good for three main things: Reviving incapacitated players if you have no other way to cure them, loading up a buffer for when you're about to run through a trap, and "paying" for divine sacrifice. Nobody will expect you to give them temporary hit points, and you'll rarely give them to yourself.
6) What do the "channel divinity" enhancement abilities rely on? I learned from playing my rogue that certain abilities have certain requirements, like melee-only attacks or weapon-specific attacks, so does "channel divinity" have any requirements other than being a paladin, or is it just a reference to the channel energy abilities from the pen and paper version?
They don't rely on anything. "Channel divinity" is just a descriptive name for the type of ability. It does not imply anything for the abilities like pre-requisites or anything.
7) Back when I was first playing a paladin (3 or 4 years ago, and he was probably not well-optimized at all), I thought being able to heal myself whenever I wanted was pretty neat...and then I started playing higher-level areas (5 or 6) and had trouble managing my spell points. Since then, I've purchased the Catacombs pack for the Wand of Cure Minor Wounds, which I imagine would be very useful to a paladin due to his high CHA modifier, which adds to his UMD score. (If you have rogue levels, does that unlock UMD as a class skill?) I'm patient, so I really don't mind waiting around for a wand to recharge if I need to heal up before moving on, and it should last me through the mid levels at least, but I know using wands is crucial for conserving spell points. So my question is this: at what point do I absolutely need to start buying wands, and how should I budget my spell points? What spells are worth taking along, and how often should I be using them? Keep in mind that I don't know anything about the game past level 7 or so.
I never buy wands anymore. I did at the beginning of my first paladin life, but on the second and third life I never bought any wands. I did buy a stack of cure serious wounds potions, but they were largely unused. Most of my self-healing was in the form of the four Lay On Hands you get plus spamming cure light wounds after killing every other mob.
The rogue level does indeed unlock UMD as a class skill. It still costs you 2 points to train a single rank during paladin (and fighter) levels, but you can train it all the way to 23.
If you really want to get unlimited mana, I recommend a torc of prince raiyum de-II. That's a great, great necklace for a paladin. (It's a guard effect that gives you ~22 spell points when you get hit, with around a 10% to proc per hit.)