You can fast travel to the peak immediately, even before making it to Sanctuary, so that is not an issue. As far as how far your gear will get you, that depends on you. You’re reading @Handsome_Dad’s walkthrough by level, so I’ll just highlight a point he makes toward the end: it’s more about strategy than anyhting else. Everything about the peak is doable in any circumstance, so long as you have a plan. Sal is generally an exception, but rocking a Deputy build I unlocked OP8 with an OP4 ROM, and @Kurtdawg13 completed the OP8 peak with level 72 gear. It isn’t easy, but it can be done. I used a level 71 Lyuda to hank surveyors at OP4, and an OP3 or 4 with my Siren to down Dukino’s mom unlocking OP7. Check the top gear thread, you may find common or farmable gear that will suffice for the purpose of avoiding a full reset before you’re ready, and Handsome Dad includes a list of easily farmable gear for most characters early in the thread. As to your last question, about doing a quest at OP0 and turning it in at OPwhatever, maybe? I read somewhere that if the last objective is “return to…” or “give x to whoever” that it does work that way as long as you accepted the mission at the desired OP level, but I’m not 100%sure because most of my gear is either farmable or non-red text. I would point out, however, that if you are using a Grog for Moxxi heals a reset would mean you had to advance the TTAODK at least to that mission to get the item again. As for being frowned on by the community, the general consensus (at least far as I can tell, I personally think this way) is that while climbing the peak anything goes (as long as you’re not outright cheating). All’s fair in Digistructed masochism, or something to that effect.
And oh yeah, welcome to the peak. It can be a real ball buster, but it’s one of, if not my absolute, favorite maps. So much enemy diversity and terrain make for lots of excitement and frustration, but if you can overcome your frustration it’s a blast.
Edited because @Kurtdawg13’s post made a point my heat addled brain forgot.