My main support is Leona, and I run her a slightly different way.
I start Health Pendant and Ward. I use 9/21 Masteries, with Armor, Resist, Regen, and Gold for all of my masteries. I use Armor Reds, Health Regen Per Level Yellows and Quints, and MR/Level Blues. Leona is in the top 5 base regen champions of the game, top ten if you include people like Singed/Mundo/Volibear because of their mechanics. With this set up, at level 5-6 you are regening enough health that you are basically under the effects of a potion-constantly.
First back is boots and wards, and further backs are for Philo, HoG, then into a Warden's Mail/Sunfire Cape/Force of Nature as appropriate to team comps. Vs. Balanced Damage, your full build (if you ever reach it) looks like Randiun's, Lucidity Boots, Sunfire Cape, Force of Nature, Banshee's Veil, Rylai's Crystyal Scepter or Warmog's.
Yes. All the health and resists and regen. That coupled with your regen (At this point, about 60-120 health per second depending on items and mana and Baron.) makes you incredibly difficult to deal with.
To start the lane, you need an aggressive trading carry, like Ezeral, Graves, or some Sivirs, or a kill lane where a high damage bruiser is paired with you (Jax/Leona is surprisingly effective). Use your regen to bait harrass, but avoid trades until 3. Especially avoid picking fights with someone like Taric or Alistair, as you can be dead before you act again, even at full health. But against a lane with Soraka/Janna/Sona, you tend to just win.
The more harass you can bait and regen away (skills wise) the less mana they have for when you start a real fight.