I've seen some confusion and misinformation about a few things regarding XIV, so I thought I'd clear some up.
FFXIV you can indeed talk to your Free Company (Guild/Alliance) if you are visiting another world on your datacenter (Datacenters are like jumbo-servers made up of smaller individual servers, and you can hop around within the datacenter but cannot visit a different Datacenter). You can still communicate with your Free Company if you are visiting another world, and you can form a cross-world party. You cannot invite a player to your Free Company, however, unless their character's home server is the same as the FC's. Linkshells don't work unless you are on the home server, and just like FCs you cannot invite someone to the Linkshell unless they are on the home server. Crossworld Linkshells however do allow for you to invite people outside the home server, and they work regardless of the world you are on.
As far as item drops from mobs, they do exist but only in the open world, and the items that drop are usually simple crafting items or vendor trash (think like bones, a claw, etc.). Enemies in instances and story missions however typically don't drop anything, and I've noticed the later into the game/higher level zones the enemies drop less.
Loot in FF is primarily based around getting treasure coffers after boss fights (whether those be dungeon bosses, raid bosses, etc.), which in general drops 1-2 equipment pieces for a random class, tokens to trade in for stuff, minipets, or mounts (varies depending on what you are doing). You also, when you are max level, earn tokens for completing a plethora of content which can then be traded to a vendor for max or near max stat gear. The max stat gear in this game can only be obtained through vendors (or in the case of the relic weapon, a long quest chain), and is character bound on acquire.
While there is some RNG involved with dungeon gear or when a mount drops in the raids, there's a built in pity system where you get tokens to get the thing you want.
Here's an example. Currently the best non-relic weapon is the Diamond weapon, which you can receive for completing the Diamond Weapon Extreme trial. It's a boss fight (kind of like a boss fight Urgent Quest, but you can start it on demand when you have a full party), and typically takes about 12 minutes to complete if you don't wipe. Once successful, a treasure chest spawns near the exit, and inside you will receive 1 random Diamond weapon, a low chance for the mount to drop, and the chance at some diamond-specific crafting items to drop. The party then rolls Need, Greed, or Pass to obtain the items. You cannot have more than one of the same Diamond weapons in your inventory, and once you obtain the mount you can no longer roll for that mount in the future. You also obtain 1 Diamond Totem (that will go up to 2 Diamond Totems if it hasn't already) per win. 10 Totems traded into a vendor will let you hand pick your weapon. 99 Totems lets you get the mount.
Armor is a bit easier to obtain. All level 80 content gives tokens to trade in for near-max stat gear, and completing the nier raids gives you coins which you can use to upgrade that gear into the strongest gear outside of Savage armor (Savage is extremely difficult content that a lot of players avoid, so most people don't go on to complete it... but it is obviously doable).
Lastly, as far as selling stuff in FFXIV is concerned, most items will sell if the price is reasonable. I've never encountered an issue putting something up and it never selling. It also doesn't take long to sell something. By the second day I've sold everything lol.