You can have as much floating or non floating parts as you want. Some game engines deal with floating parts better than others, so you might have some lighting issues with floating parts. A good start place is anything that moves should be floating and baked seperately. You can have a piece like that as many floating parts…
So currently on my high and low poly model the rails on the side are three different parts and are basically floating geo. Do I need to combine the 3 parts into one parts on both models?Also do I need to add this geo into the low poly so its not a floating?