after all the research i did for putting my 220 on a 2nd floor, i wouldn't go over 150g without adding jacking posts. i wouldn't be surprised if a 150 longterm did some damage to your floor as well.
don't forget to include your sump/topoff/fuge in your total gallons
1st floor is no stronger than second floor (unless it's on a slab). It's just easier to reinforce because the joists are usually exposed in the basement.