What tool should I use and how do I learn about it, would google suffice?
You can learn how to use dnspy, cheat engine to start
is this activity considered a crime? regardless I still want to do it just to study
Depending on you country, but usually no.
Does it make any difference to test tools in single-player or in multiplayer that can put me on the ban list?
Singler-Player is better cause you dont have to worry about people reporting you.
Is not 100% random when you loot, depending zone, Level and where are you looting (Normal Loot spot or enemy loot)