It won't make any difference to the SEs when you post the videos. They'll index them when they find them and each individual video will be ranked on its own merits according to the SE algorithm (which doesn't care many other videos you've distributed or how long ago it was when you posted the last one).
So post them at whatever frequency makes sense for your human viewers. Presumably, you want real people to watch these videos, right?
So figure out how often it would make sense to post to give the best impression to (and get the maximum benefit from) these human viewers.
Right off the top of my head, this would be my recommendation (you should take this with a grain of salt and vary as needed to fit with what you perceive to be your target audience's expectations):
If these are rather long, information-intensive or instructional videos, it might make sense to post them one a week (or even longer apart). This will serve two purposes for those who are following along as you post them: it will give them more time to digest the information in one video before you hit them with another, and it will give them the impression you're spending a bit of time putting each video together (which will, one hopes, increase their opinion of the quality of information contained in the video).
If they're lighter, entertainment-style videos, I'd say to go ahead and post them as quickly as you want... unless one of them really seems to be "taking off," in which case you might want to hold off on posting the next one until the "hit" seems to be tapering off a bit so as to not have your next couple of videos be lost in the shadows of the "hit."
Of course, for people who come along after you've begun posting the series, it won't make any difference; they'll find them all at once anyway.
--Torka