Breton mageblade seems like a pretty fair choice. If you want to sneak (assuming you mean cloak) forever and ever, you'd be looking at increasing your magicka recovery specifically, to the point where your magicka recovery is greater than or equals the cost of cloak. If you mean sneak without cloak, you're looking at sneak cost reduction, although that's only really necessary in my opinion if you sneak A LOT and have pretty much no stamina (which is fairly standard for most magicka builds).
Magicka DPS and magicka healer are fairly similar in builds (presumably you're not rolling a tank), so light armor is a good choice. Due to the passives though, I'd highly recommend only 5 pieces of light armor, and either running 2 heavy, or 1 heavy and 1 medium piece for the other two slots. The heavy will help a little bit with your squishiness, and medium can be used for the undaunted passive (you know the one). This is fairly standard.
CP location is mostly up to you - focusing a bit on spell crit is a good idea - and PVP faction is really your choice. The PVP leaders are always changing - a LOT if you play the game as long as I have - so it's best not to base your faction choice on the current PVP leaderboards. If you are running a DPS build for PVP though, I do highly recommend putting some points into spell penetration in addition to your other damage stats. Generally, avoid anything to do with physical or weapon damage or stamina. You only need points in damage, and just enough health to not get one-hit constantly.
Vamp is alright. Try it out.
Outside of that, welcome back. : D