Is this game like online so you can fight other players or can you group with other people to kill larger things to get vauble stuff?

At the moment, there is no actual 'PvP' mode (Player versus player) in FFXI, apart from the optional Ballista game. But you have to be significantly high in both Job level and Nation Rank to get a Ballista licence in order to play it however.

As I don't play Ballista myself (on account of my lowly level and social rank :-( ), I don't know what it's actually like to play though.

It's not really "that" high of a requirement to play Ballista. In fact, if you manage to actually find people to do it, you can play with just a level 10 job... but you'd instantly find that it is pretty limited and quite boring when you have Black Mages and Monks dominating the field.

This, of course, is Diorama Abdhaljs-Ghelsba, a Ballista arena located off in some undisclosed location around the Tavnazia coast. All you need is Chain of Promathia installed and registered and you're good to go. You don't need a Ballista License to do so.

But, for the bare minimum for Official Ballista, you need one job at level 30 (pretty easy to get to) and Rank 3 (really easy if you have friends to help you with missions).

For the most part, FFXI is mostly a co-op game. Because of that, the game is centered on a system that is meant for cooperative play instead of competitive play. Ballista is nothing more than a mini-game really since the game can be really unbalanced and eventually, really boring. It is an aquired taste though but it is just simply recreational and nothing much is to be gained from Ballista.