So can we become a Vampire Lord as many times as we like a day for as long as we like?

I think that's the case. Though we won't no 100% until the Beta is released, at least.
There will probably be a cool down worse case scenario. But it's said you can turn into at will, and leave at will. So no time limit like the Werewolf.

Probably

I'm interested to see just what powers we can use without transforming into the vampire lord. Also be interesting to see how the normal vamps compare.

Possibly only unlimited transformations if you get certain item.. sort of like for werewolf..
Only guessing but it would make sense to have some sort of balance