For each of those in turn...

I wouldn't go for full DL. It takes too long farming CM to do that, plus, it ignores all of the loot in the WP/AK/HM tiers which are excellent stepping stones to higher tier content. I would do your daily roulettes (low level and main scenario, at the least; don't unlock HM Copperbell, HM Haukke, or Pharos and you'll always get the super easy WP/AK for your high level roulette) because that nets you 600 philo tomes each day along with 80 myth tomes. After finishing those for the day, I would run AK/WP since those give just as much philo tomes as CM/Prae, are generally faster, and provide you with i55 loot. Which gets us to...

You should start working on it as soon as possible. The starter weapon is super cheap now so it presents no obstacle. Chimera can be done with half of the group unconscious, as long as the conscious ones are paying at least the slightest attention, and Party Finder makes getting a group a joke. You should be trying to run AK anyways, and Hydra is only marginally harder than Chimera. The HM primals themselves aren't too hard either, with the primary limiter being the ilevel requirements (which means that you'll have to farm up a bit of gear just to get in 'em). If you can find a good LS/FC, you can often just get carried through them as soon as you meet the minimum requirements; sometimes, you can even find a random group that feels like carrying someone.

DL accs are better and provide an excellent cushion to get your myth/allagan accs. Plus, they're easier to get than the HM accs because you buy them rather than trusting the RNG not to screw you over (I think I've seen the Hoplite Ring twice. Ever.). I would probably get the myth ring first since you can only get 1 DL ring and the myth ring is BiS anyways (plus, it's cheap enough to buy your first week).

It depends. It depends largely upon your BiS. You want to maximize your parry rating while staying within a few points of 482 acc and getting as little skill speed as possible (speed stats are terrible). There are multiple loadouts that I've seen people use so it's left to your judgment.