? How do you get $29.99 by adding $9.99 and $9.99???
As for going beyond that number, for now, it doesn't matter...at some point in the future when it does matter I believe I read that it would still work, but processing would be slowed until your next reset date or you'd have to either upgrade to the next level or buy more credits. Not sure that detail has been decided yet...or at least published and for now it's irrelevant.
This is not a existential threat to our existence...try it out, use it and see if it's something that will benefit your photography...if not, continue what you're doing...