"Please answer me" is not a good topic name. I changed it to something funnier.
1. The code doesn't support convertibles or bikes. You could replace a car sprite with a bike but you wouldn't be able to fall off and it would look like it always has a rider or never has a rider. There are some tricks that could be done to fake a rider but it's just not going to be like GTA1 or games with real bikes. Bikes probably weren't in the original design document and they didn't have time/budget to add them. They weren't great in GTA1, so they probably just decided it was easier to leave them out than make them great.
I don't know much about San Andreas mods. That topic is locked, so I guess you'd have to create a new one in San Andreas section to ask.
No one has found a way to move the camera out of top down view in GTA2 (even if you could, it wasn't designed for that, so the performance would be bad and all the vehicles and characters would be in 2d (flat).