a couple things (that i haven't seen mentioned, or maybe i missed):
1. if you're inhaled and spit out, if you rotate (move?) your control stick while you're in the 'star' you will break out much faster than not doing anything (read: closer to the ledge) and after you break out of the star, you always jump and still have a second jump available. i've only tested on FG at low and high percents, so firm confirmation about the control stick break-out would be appreciated. (as a side note, i suggest only moving the stick as opposed to button mashing because if you get caught using an aerial after breaking out you lose valuable recovery time.)
2. i've had problems with jab reflecting gordos as well, but i think the problem is because a) my jab is stale by the time i'm trying it (in other words, at the beginning of the match, you should be able to reflect gordos with infinite jab no problem); or b) the multi jab comes out and that will not reflect the gordo. i've mistimed ftilts online as well, so generally i go for a reverse utilt to reflect gordos.
3. kind of related to ^2., i find that dedede's approach is quite terrible, so make your opponent approach you as much as possible. after throwing a couple gordos and getting them reflected back at him (watch out because they can still reflect it back at you by hitting it), usually they will opt to approach, where imo they are at a disadvantage. most dededes on FG will roll into you and try to dsmash, dtilt, or grab out of it. catch them on their roll with a dsmash. if they run forward you can expect either a dash attack or grab, so be careful with your response as a dash attack will punish your spotdodge if you expected a grab. some dededes will float above you, wait for you to throw out a laggy usmash and then land on you with a nair and cover their landing lag with a dtilt, jab, or utilt. shield is an okay option if that is their game (oos upb?), but watch out for the tomahawk grab. (fun fact: inhale does not beat a shield that covers your hitbox) a good dedede will mix-up their approach with mixed-trajectory gordos/tilts/jabs, taking a little bit of stage control at a time. with that approach, play smarter (read: you're screwed), because a good dedede will be a difficult match.
4. against a good dedede, never try to recover on-stage in front of a charged fsmash with a counter unless you absolutely have the read, because you will get waited out and die at 20%. if possible, it's better to go for the ledge if they're charging the fsmash. (don't get scared of the gordo they throw out to discourage going for the ledge, you can often avoid it)
EDIT: 5. dedede can only jump in midair four times, so if they're floating above you, you can expect something after their fourth midair jump.