Only the full suit of armor has a capacity. It's 8, and the matching helmet has 4. This is listed in arsenal. The rest of the stuff has no capacity, so it uses the standard rule of 6 or 1.5x the highest armor rating worth of mods, where each rating of the mod counts for 1 point. A 6/4 piece of armor can have up to 9 points of mods, so that'd be a rating 6 thermal and a rating 3 nonconductivity. Things without ratings just count as 1 point.