Few questions about CoreXY

Hello,

I am planing to build a a new printer completly by myself and want to build one with CoreXY Systerm and I basicly understand that.
But I still havew a few technical questions about it.

Do the belts of a CoreXY Printer have to be perfectly square or does it matter if they are rectangular?
Do they have to be perfectly straigt or can they be skew?
Do the belts have to be inline on the moving Part (Extruder) or can they be mounted on a different edge of the extruder carrier?

What do you think is the best way to build a CoreXY Printer?


Thank you,

Plermpel