Epicurus uses "imperishable" specifically to describe the gods. He may use those terms elsewhere, but that's what I'm remembering right now.
Yep. There's just too many clear statements in the texts to think he was being totally allegorical.
As for immortal and imperishable I suppose part of the issue too is whether they were deemed "eternal" as having existed from the infinite past. I don't know anything clear on that . It's tempting to think that they too "evolved" over time, but we're faced with the same issue of time stretching back into the infinite past, with the implication that whatever is now, could/should have also existed somewhere in the infinite past as well, since there is no reason to postulate (and probably it's the reverse, in fact, many reasons NOT to postulate) a single "starting point" for them.
(Again, as a class, not necessarily as individuals.)