1. I assume the bonus AC from the mounted combat feat is like tumble bonus, marked as other and stacks with all AC?-A.C. changes
You no longer gain tumble A.C. whilst mounted. (Because whilst you can dodge out the way, your horse cannot). This can be offset by your ranks in ride on a 1 for 1 basis. So 30 ranks in tumble and 8 ranks in ride will get you -5AC.
With the mounted combat feat you ALSO gain 1AC per 5 ride ranks. (Mounted Combat feat now enabled - see below)
-AB Changes
If you have the mounted combat feat you gain +1 AB per 8 ride skill (incl Dex and equipment) to melee weapons when mounted. This is capped at +10 for 80 points.
If you have the mounted archery feat you gain +5 AB to ranged weapons when mounted
2. Is the AB bonus included in the max +20 AB bonus from various sources?
Sorry if already explained somewhere, couldn't find it.
Thanks in advance.