So my Nord, Benedikt the Drunk, made it to Kvatch but quickly found that he was no match for the Gates of Oblivion (being only a weak Level 2). He turned and ran . . . but now I'm wondering, will the quest still be available when he's stronger, maybe after a few weeks? Or will he no longer be able to go back since he already saw what was happening? Did he miss the opportunity?

You can go back later, at any time. It'll get harder before it gets easier, though. Don't go back before level 20 if level 2 was too hard.

Takes so long to level up . . .

You can postpone the Kvatch quest indefinitely. That's what's so funny about it. Savius will implore to to "GO SAVE KVATCH NAO!!!" but if you want to let three in-game months pass before you do it, its fine.

I would recommend, though, is to save enough gold to buy enough healing potions (strong potions of healing would be good).

Out of curiosity, do you think it's even possible to finish the main quest at a low level? I only went there because everyone said to complete the main quest first and get it out of the way.

If you can't do an Oblvion gate at lvl 2 you may want to re-think your character, your tactics, and/or your gear. Quite a lot of free stuff is available if you join and explore the fighters and mage guilds. Don't expect to automatically get stronger as you level. Alchemy and the enchanting/spellmaking altars are your friends though.

Mara

There are videos of folks that have done the mainquest at level one. its all about being prepared, and having the right equipment.

Well, I didn't really even try hard haha. I suppose if I planned ahead I could do it.

You have to exploit a certain work-around to finish the MQ at level 1, though. The minimum level for a Deadric quest is level 2, so technically you need to be level 2 to actually follow the quest through to the end.

One of my characters did it at level 2; it's actually pretty easy that way, because you only have to deal with low-level daedra, who have very limited types of attack. Basically, at low level, you only really need to shield against fire from all the scamps and fire-towers, from direct melee damage, and from some minor elemental attacks. Hint: a dunmer (dark elf) has built-in fire resistance.

Nords are my favourite characters because they are incredibly good as melee warriors (50+ Strength AND Endurance!). However, they do lack the magicka for most useful Restoration spells, so I would definitely suggest buying (and using; do not hoard as items quickly lose value as one gains levels) potions and using alchemy to make potions. Good luck!