In that one I'd use the future continuous for the final verb, to match the second one: you're talking about two things that will both be happening together in the future:As soon as you get into the habit of doing sports, you will be running around all the time, because you body isn’t/ won’t be holding you back.
Which one should I use “your body isn’t holding you back/won’t be holding you back.”
I'd use the future continuous in that one too:Can I go slower when I am entering the highway?
Absolutely not. As soon as you/Once you go slower, you are blocking other people’s way.
I think “you are blocking” works better than you “will block” correct?
No.Once you stop spending money, you can buy more things, because you are not constantly spending any money.
—> refers to the moment I stop spending money.
Once you stop spending money, , because you won’t be spending money constantly.
—> only refers to the future.