Anyway to answer the question every job I play fits across 28 Slots.

So crossbar 1 holds 16 and crossbar 2 holds the other 12

If you consider that each cross is split into 4. On the 1st part I have my main combo, 2nd part, additional damage weaponskills/dots etc 3rd part Buffs, 4th Part OGCD's (this is also just a general guideline)

Then crossbar 2 - holding down L2&R2 gives me slots 1&2 on the 2nd bar 1 holds any healing or defence buffing skills and 2 holds my AOE skills, The expanded hotter gives me access to slot 3 by double tapping L2 which holds sprint, LB and 2 remaining lesser used skills

So there we have it 28 skills without ever having to switch the cross hotbar