Basically when you go to another location to catch pokemon and stay there awhile the only thing that can get you softbanned is when you try to catch one and your gps rubber bands at the exact wrong moment, causing you to get soft banned.
As far as pokestops are concerned, as long as you wait the appropriate amount of time before going to a location from your current location, you should be able to spin stops as much as you want. THEN you need to wait the appropriate amount of time before switching to another location to catch pokemon or spin stops.
Spinning pokestops is alot different than catching pokemon in that you actually have to be at the pokestops location to spin it, therefore if your gps drift obviously the stop won't be there, so no softban.
As far as stops go I have never been soft banned just spinning stops. There are times when your gps will lag and you won't be able to spin them, but in that case you just need to wait a bit then you can spin again.
Honestly if you need a location where the stops seem endless I can't think of a better place than a place that someone posted on this subreddit. Here is the post.