With all the snow I want to book a FL trip asap. Will it be warm enough in Naples area mid-March to go in the gulf beach water, or should we push back to April
We're going to stay at the Registry Resort...

I'd say wait until April, but as a native Floridian the gulf isn't warm enough for me until late may.

Sorry no guarantees. It isn't warm enough for me in the Gulf until about July, but there will be a ton of northerners in the water by March. In fact on my beach walk this morning, I was surprised by a fair number in the water now.
March SHOULD be warm -- in the 70's and even the 80's. But there is no guarantee that there wouldn't be a "cold spell" in the 60's, or even lower. April is similar, maybe a little less chance of the cold spell.

The later you travel the greater the probability of warm weather. Push it to April/May if you can. My favorite times to visit Southwest & Southeast Florida are May and Oct (risk of hurricanes in Oct but over the years we have been very lucky).
Mid-March can be downright cold! On the other hand, it can also be warm but not guaranteed. Why don't you go to www.weatherunderground.com & do an historical weather search? That may help you decide what to do.

I looked at the weatherunderground.com website (thanks) and it appears the ave. temp would be 78 degrees or so. I would categorize that as warm enough.
We were in Orlando in May once and it was oppressively hot...couldn't do a thing!
Anyone else's advice?