Thank you.
First of all, fully automatic firearms are ones that continue to discharge when one pulls the trigger. The firearm continues to discharge as long as there's ammunition, so they are basically what most people would call a “machine gun”. Those have been illegal for private individuals to have since 1977-78 approximately. There are a tiny number of people who still own them because these were grandfathered at the time, but those people are now extremely old. Well, they are even older than me, so I call that “extremely old”.
Then to your question about what would be an assault-style firearm, it would be a fully automatic firearm that fires an intermediate power cartridge. Hence, the original assault rifles like the German Sturmgewehr or the original fully automatic AK-47s are assault firearms.
Now “assault-style” takes it a step back. Basically, they're suggesting it is anything that looks like that. Because some people have different tastes, you can buy a kit that will make a rifle made 150 years ago look like one of those military-style assault firearms simply by changing the stock and putting some accessories on it.
I'm not sure I got all of your questions. They were fairly long.