A “Kit” is a collection of 4 sounds (=4 “Tracks”). A single “Pattern” has triggers for all of those 4 sounds. When you select a kit, the machine sets the current pattern to use that kit.
So, if you want to make a small modification to a sound to have a slightly different kit, it needs to be saved with another name. You can have two identical patterns, e.g. A1 and A2, but have them play different kits.
Don’t know about 3), since I haven’t touched Overbridge yet…