Ok, so I have a Breton Mage with the following major skills:

Alteration
Conjuration
Destruction
Restoration
Blunt
Sneak
Mercantile

I am currently playing Oscuro's Overhaul and I find my character to be too weak physically. I started contemplating playing as a vampire for the nice boosts becoming one provides. I need advices first though. Is playing as a vampire any beneficial? Is it fun or just tedious? What do you recommend me to do and what stage would it be best to play at? I have Vile's Lair installed. Any help will be appreciated. Thanks.

I'm going to level with you. Vampirism in the original game is just awful. Since you're on a PC, I highly recommend getting a mod for vampirism. Google search Unholy Darkness and that will make you want to stay a vampire.
It's a very slow progressing journey, so get vampirism as soon as you can. You get much more powerful as the days go by.

I also recommend getting http://www.tesnexus.com/downloads/file.php?id=15697. That way, your character won't look so ugly.

Ok thanks. Good thing I'm on PC too.

Normal, I would tell you not to. But you seem to have the mods for it.

Even vanilla has plenty of benefits, the only strange thing is that the more you feed, the weaker you get. I stay 100% vamp for this reason and never feed.