You should be a force worth fearing, but beware, you can be taken down fairly easy.

Good communication is a must with this build, and if your team is backing out/off, you need to be the first one to get out so you aren't targeted with the skillshots chasing retreaters. The only time you should get close to your allies is if you are inturrupting a channeled ultimate, (ex Nunu's Absolute Zero, or Katarina's ultimate), which every good Soraka should be. If you have the upper hand in a team fight and are getting them in a retreat-defensive position don't be afraid to unleash starcall on them to tear off MR so your team can dps more.

This build is not for a beginner player, as it requires awareness.

A good balance is mandatory between AP/MP5 as a support character, too much MP5 and you lose your healing ability, and with too much AP, you could run out of mana much quicker, irregardless of if you use infuse to restore mana, because that is not infuse's only job. You need it as a silence too.

I feel this will give you a good amount of Magic Resist, Ability Power, and Mana Regeneration.
If you feel that for higher elo play, you should get more gold per 5 items, by all means do it and sell them later.

Nothing is mandatory past Rod of Ages, and if you want to grab a Mejai's Soulstealer early in the game for a quick AP boost, that is also effective. I play without a gold item and last-hit when my ally needs to return to the base, and I get very similar results to 0 CS players.

Starcall is just not for supports early game, there should be almost no reason you have it, for two reasons, one, you need to leave farm to the carries, and two, the only people building magic resist early are tanks, so whats the point in that?

You need the points in astral blessing and infuse, there is just no alternative.

I've been told that Heal/CV works wonders in teamfights, Heal+Wish is GREAT AoE healing for level 11-14 team fighting, although heal begins to lose its edge as the game goes on.

The other alternative is Ghost/CV, with the mastery point in ghost.

PROS

Easy to shut off harassment early game.
Allows the non-mid carry to get more farm and be able to stay in lane much longer.
Gets that lane an edge on expirence as they only have to return to the base for items.
Obsoletes a jungler with constant warding.
Allows incredible survivability in team fighting.

CONS

Lacks DPS.
Very squishy-easy to be focused if not used correctly.