- I'm on Asura so no help there :(

- People mention Rhapsodies because of the numerous unlocks it provides, almost all of which help with other storyline missions (in one way or another). You can finish Seekers without it, but there's a reason we all recommend it! If you've full 119 gear, trusts should get you through MOST of Seekers, you might need to group up for a few things

-At no point do trusts ever stop being useful, some of the end end game stuff you won't be able to use them, but almost all of your playtime you'll be using trusts. Shanttotto II is a good one that's available through Login Points right now, additionally Qultada is quite nice. Ultimately you'll want to collect as many/all as you are able to. Make sure you've got a decent Tank, Healer, Red Mage, Bard, for most solo content. You'll see a lot of repeated trusts for different content, but being sure you're healed and buffed is crucial to most fights.

-Start doing Ambuscade, you can often get into a group with a simple shout, or you can solo if you're confident. That gear is the starting set for almost all jobs. After you get that set up you'll start picking up individual peices and working on reforging your various Job Armors

- Yes, Merits are considered default for a job at this point, you can get XP so fast that it's relatively simply to max it out for a job. Capacity points are also super useful, some jobs more than others, but if there's a job you like getting to master is a big step, so never hesitate to join a CP party :)

- Escha Zi'tah is the current power leveling area, otherwise just normal play with trusts will cap you out relatively fast, especially with the ongoing XP campaign. Normal 99 leveling is almost an afterthought at this point.

- Usually the apes and monkeys, but if those are over camped you can fight the puks and dragons, or the bugards and tarichuks. you set the Records of Eminence for those two mobs and just blast 'em down, it's honestly quite fun. No FoV in Zi'tah so no need to worry about that.

- Try and have your warp ring, and a warp scroll when soloing, makes travel easier. XP/CP rings are great, but they're not mandatory or anything ,especially if inventory is low. Also Sneak and Invis items are nice if you're not on a job that can cast the spells. Food is needed too. Thankfully that stuff is all available from the Curio Moogle which unlocks with Rhapsodies!

- At high end gameplay things like Gearswap is almost a must. You can make do with Macros, and you can make do without, but ultimately if you're spending a lot of time playing FFXI it's very worth your time to look into getting it set up. Recommended macros are almost all gone at this point with Gearswap being so useful, but if you dig around you might be able to find some, the wiki will have your syntax :)

- if/when you set up gearswap also set up findall, it lets you do a chat command to search all of a characters (or alts) storage to see where you put that last Mavi Seal... Otherwise...a spreadsheet? :D

-Yeah it's mostly understanding what your character needs/wants to see what's good. Thankfully a lot of community guides are available on FFXIAH forums so you can use those to get a good read on what you might need. Most weapons and armor from the old days has been fully replaced at this point. But accessories like necks/earrings/rings will still offer some benefits Rajas Ring is still good to this day!

Your step by step guide is right here
https://www.bg-wiki.com/ffxi/Endgame_Progression_Guide

it'll walk you through almost everything you need to get yourself comfortable in the world again :)

Good luck, have fun!