1) Getting to LV 50 in normal mode could be compared to self-torture.
2) This will let you do all the other three at once
3) See 2
4) See 2
There's really no reason to complete only the storyline and, afterwards, the side missions, unless you're aiming at getting a particular reward scaled to your level (most of the times, dropped loot is FAR better), not to mention rushing headlong into the story in TVHM can lead to being underleveled (which is why you might want to get maxed out in normal mode, although it'll take a handful of time...).
Also, you're missing out on the game's additional content, which for once actually adds quite a lot...
- Mechromancer and Psycho characters, which are bloody fun to play;
- 4 entirely new areas, with weapons, enemies, missions, challenges, raid bosses and their own storyline (Captain Scarlet's pirate booty, Mr. Torgue's campaign of carnage, Sir Hammerlock's big game hunt and Tiny Tina's assault on dragon keep)
- Extra arena (Creature Slaughterdome)
- Ultimate Vault Hunter Pack 1 and 2, featuring a little new area for a raid mission (Digistruct peak), 30 extra levels (22 base levels + 8 "OP" levels, bringing max level up to 80) and an extra difficulty (Ultimate Vault Hunter Mode, which I love to dub "Ultra Very Hard Mode")
- Skippable but fun holiday and BL1 related extra bosses (T.K. Baha's Bloody Harvest, Halloween; The Horrible Hunger of the Ravenous Wattle Gobbler, Thanksgiving day; How Marcus Saved Mercenary Day, Christmas; Mad Moxxi and the Wedding Day Massacre, Valentine's Day; Sir Hammerlock vs. the Son of Crawmerax, BL1 related)
Steam's offering everything for up to 70% discount for another 5 hours, if you're interested. Otherwise, you can pretty much stop after finishing TVHM