2. The important factor to change muscles is load bearing. If the load makes you push only 8- 12 times at a time, you can't push it. This load is very good for increasing muscle strength and size.

3. The general standard barbell is composed of several barbell pieces with different weights. You should be able to do it by adjusting. If your barbell can't adjust its weight, buy a standard one, or tie something heavy on both sides to make do.

I hope the above answers will help you.