Yes. There is a small chance that it could scratch a wooden floor but you can buy sticky bits of felt to protect the floor, or use something like an old towel.

Yes, all parts are the same for connecting. From 3 to infinity, it says itself

There are 8 elements and from these elements you can create any shape, so also a U Example 3left x2down x3right at a U

yes, the width is small enough, if the rabbits are not smaller than 5 cm in diametre.