New Owner, a few questions...

[NH93]

I would bump those temps ASAP!! Should NOT be below 75F! Bump the ambient to 80F and hot spot to 90f!
I am not familiar with tubs, so I cannot help much there. To me the 16gal sounded right for the age of the snake, but they vary so much in size when they are young. Personally I would have kept her/him in there and blacked out 3 out of 4 sides with dark paper, and added much more decor. You probably need to add a 50W red bulb (just UVA, not UVB) to bump those ambients - only in the glass vive though. The humidity should be around 60-70%, and 80% only for shedding.

What happens with temps too low and humidity too high, such as potentially in your case, is respiratory infections. This is why it is important that you bump up those temperatures about 5 degrees F for both the cool and warm side.
If you add a heat bulb it will decrease humidity as well. Also, digital thermometers and hygrometers are essential because the dial ones are incredibly inaccurate. You'll want a probe thermometer to measure where the UTH is. You can look at the care sheet on the main page for more info on how to do that correctly

On that note, I find it hard to believe that in a glass vive with paper towel that the humidity would be 80% (or anywhere close to that); in which case, your hygrometer is probably inaccurate, or you live in a VERY wet area of the world! On the plus side, this means that those low temperatures that need to be bumped up aren't as hazardous. But they are not only important for RIs but for digesting food as well. Keep in mind that ball pythons are from the forests of Africa.

You should be feeding to the widest part of the snake's body; i.e. matching it to the width of the prey, or 10-15% of the body weight. I'd stick with rats. If you can find a size smaller and a size larger to try out, that would be what I would do. When mine stopped eating for a month (and he should be on the small rats but he's still on weanlings), he got nervous of the weanlings and I had to jump down to pups for 2 weeks until he would eat consistently again.

Offer about once a week as you have been.

Just remember to really clutter up that vive with hides and decor (could be tissue boxes and crumpled up paper balls, doesn't have to be expensive) for security, and black out the sides and back. And BUMP THOSE TEMPS!
One final note is, don't handle until s/he has eaten a few times for you. I know it's difficult... but really try not to. Ball pythons can be picky and can stress easily at times, and the first thing that seems to happen when they are stressed is they stop eating. Because s/he's been moved around now, I think s/he'll need more time to settle in. It might take some time so be patient.

All the best!