From what I've seen in gameplay videos, it looks like the vampire lord relies quite heavily on Magicka. Is it worth it for a character with only 100 magicka? I know you can go on the ground and use claws, but can you sneak attack and stuff?

walking is more or less your 'stealth' mode as a VL. there is no active sneaking. You want stealth, use your normal body. You want monster class baddassery, shift to VL

I don't think so, I have a warrior vampire with 100 magicka, but in VL form I have 350 or something like that.

So, it GIVES you magicka?

yes it does

There is also a perk that reduces your night magick and blood magick casting cost by 33%.

It's still fun, my character has only 140 but still kicks ass, but I would stick to night time as the daytime penalties are bum.

Also lets just say that as you do the side quests you become more powerful and magicka becomes less of a problem... I would say, but I do not want to spoil anything (even though it's not a central part of the plot). It's enjoyable watching your power grow.

I have 1,110 magicka when I am using enchantments with my regular character, and with the ring of recovery, amulet of akatosh, royal vampire armor, and morokie my magicka regen when added together is 350 but it does, regenerate as fast as you think it would.