1) You can be in up to 8 linkshells at the same time. They will all show up in your chat log with the number next to them. You can also change the color of the text of each individually to further tell them apart. Other players cannot see what other linkshells you're in.
2) Grand Companies are more similar to factions in other MMOs. They're part of the storyline. What you're looking for are the Free Companies, which brings me to (3).
3) A Free Company is the more traditional guild system. You can only join one, and Free Companies will get different perks like FC only missions, crests, and a guild hall. We don't really know a whole lot about them yet, they're new for ARR and aren't fully implemented yet.
2) Grand Companies are more similar to factions in other MMOs. They're part of the storyline. What you're looking for are the Free Companies, which brings me to (3).
3) A Free Company is the more traditional guild system. You can only join one, and Free Companies will get different perks like FC only missions, crests, and a guild hall. We don't really know a whole lot about them yet, they're new for ARR and aren't fully implemented yet.
