Yes the more fat you have the more muscle you will have to support that extra fat.
Without steriods the average person can add only about 10 -15 pounds of pure muscle a year. Everything else will be fat.
One of the things that confuses people is though you do absolutely control the amount you weigh, you do not control where it goes.
For instance, I know many people of Puerto Rican heritage that happen to store their weight all over fairly evenly. (I do realize this is a generalization, it wouldn’t be hard to find exceptions). If you’re overweight but have fat in your stomach, your butt, your legs, your face, you’re still gonna look proportional.
This opposed to the guy who is rail thin but has a gut that makes him look pregnant. That bubble butt is nothing more than fat being stored in a place people think is attractive rather than the stomach.
Now there is a technique for adding additional muscle without steriods that seems to work for some people. As I said in general you can gain only 10 - 15 pounds of pure muscle per year, without steriods. But if you eat A LOT just shove it in, you will gain almost all fat but you will gain muscle to support that fat. Then you crash diet to lose it.
What happens is you will find you can gain a bit more muscle per year that way. Maybe 3 pounds. Now that’s not a lot and frankly most people can’t lose the weight once they cram it on, and it’s definately not healthy.
You have to remember that bodybuilders do it because the extra 2 or 3 pounds of muscle can make the difference between a first and second place finish. This translates to thousands of dollars for them.
For the average Joe, that technique ain’t worth it.
As for bone density, yes it does increase. This is VERY important to understanding why steriods are bad. Steriods allow more muscle to be gained, than you should.
When you left weights you are telling your body to increase the muscle to accommodate this. But the body also increases the density of the bone as well as the flexibility of the tendons among other things. When you use steriods, you increase the muscle, but do nothing to increase the bone density or flexibility of the tendons. This is why steriod users easily break bones and tear tendons.