I was wondering if each craft can be useful for every job - or if they are tied to aiding specific ones. (for example WoW uses blacksmithing for plate classes, tailoring for spellcasters, etc).
Certain jobs benefit more from certain crafts than others. For example, if you wanted to level Ranger, you might want to level Woodworking so you can craft your own arrows. Or if you wanted to level Corsair, you might want to level Alchemy so you can craft your own bullets.
As far as gear, whatever job you choose to play, chances are that you will need gear from more than one craft.
I recently learned that you can only have one at 100, so.. my plans for fishing + crafting are out the window :(
Fishing and Synergy are exceptions to the crafting skill limitations in place. You can take Fishing and Woodworking both to 100, and that would allow you to fix your own Lu Shang's Fishing Rod when it breaks. Or you could take both Fishing and Cooking to 100, and turn the fish you catch into food instead of simply selling the fish directly. Or you could take Fishing and whatever other craft you wanted to 100.
Also, SE has stated that they are looking into increasing the limitations on crafting skills, so that you could take 2 (and maybe even 3) different crafts to 100. "Synthesis: skill cap adjustment" is shown on their roadmap as part of the major update coming in May. So it sounds like they may be implementing this sooner rather than later.
Is there anywhere I can go to view more detailed info on FFXI crafting? I just want to know what crafts are best suited for thieves, dancers, ninjas, black mages and white mages. (the jobs im contemplating playing).
I don't know how outdated some of the guides and stickies in this forum are. But you can probably find some general information that still holds true.