The problem is that FFXI characters are just too complicated. We're not confined to one job, or one nation. It's impossible to show everything, so keep it simple.
One nation I think is ok, because although you can change between them, most people don't change super often. Sure I'm Rank 10 in all 3 nations, but I'm Bastokan through and through.
I would suggest Name, Server, Rank (your nation or possibly all ranks), and one job. Of course I would like multiple jobs to display, but if I can't have all I think sticking to just one would be best. I think most people have one job that they consider their main, or they like the best, or best represents their character. People can still add a text portion to their sig beyond the standardized graphic and then they can put all the additional info they want to tell people about.
It's impossible to make everyone happy, so if you stick to the basic things that don't change (much), then at least everyone will be equally unsatisfied. :)