First welcome back to your addiction.
The server doesn't need anymore jobs, most people have multiple jobs at 99 and/or dual box. However, play your game to enjoy yourself. So pick whatever job you enjoy most, other then RDM (game wide) not being a job invited for any event you will get into eg events easily enough and low man all there used to be.
There are a number of LS that are newbie/returning player friendly. Dispite me being being a jerk, the one I am in is helpful and fun. Social by nature with members group together to get events done. Message me if you are interested in a social shell and I can direct you to a sackholder.
From what I have seen no updated guides. I came back in Oct and had to just look things up and ask in game. The ls you join will help you get caught up. I was away for close to 5 years so Abyssea and procing were what I hard to learn from scratch. Get into it and its easy to pick up.
What job do you enjoy most? Leveling is very easy and fast now, so if you have three favorite jobs getting them to 99 won't take years.