There are 3 ability types, Mind, Muscle & Power.
You can only
unlock character ability points by leveling up, and you only get 1 Ability Point per level up.
In total, you are going to need to reach Level 80
to be able to max out all the abilities for the achievement to unlock.
If you want to get this fast, there is going to be some XP grinding involved, even after you have completed all the campaign and side missions. I was only circa level 50 after completing them.
As of writing this, people are saying that the best method is to replay the 1st mission over & over again, because it is short and has a decent XP reward. I have created a video showing a 100% stealth run which will give you 3 x No Alarm XP Bonuses!No Alarm Bonus 1:-
After you unlock the coded door.No Alarm Bonus 2:-
After you lift up the heavy yellow door.No Alarm Bonus 3:-
After you flip the switch and pass through the high security door.
If you do this on 'Challenging' it will grant you a healthy amount of XP & Silver Coins at the end of the mission. The enemy AI is fairly predictable, but it can sometimes change. As for your AI sister, she can be annoyingly slow at keeping up and will occasionally set off the alarm.
You don't have to copy my exact run, but just make sure you stay hidden while letting your invisibility recharge.