Power feeding is generally used on slings personally with a G.rosea I wouldn't advise to do so as Grammastola are known for fasting G.rosea being the most notorious for it so If you want it to eat regularly I'd say go with 1 a week unless it's abdomen is rather large then I'd drop the feeding rate to try and lessen the chance of a long fasting period, being a rosea though it's Gunna fast at some point it may be 1 month it maybe 18 months depends on the individual make sure it has a water bowl at all times as they can go a long time without food but will dehydrate without water.Congrats on the new T. My first T was a G. rosea. She was a gift for my 14th birthday. Although a very common species they always seem to be very full of personality.
It all really comes down to the size of your T and if it is not yet an adult how fast you want it to grow. Feeding your T more often speeds up their metabolism and causes them to molt/grow faster. It is also said to shorten their life span, but there seems to be no sure consensus as to if it is by a significant amount or not. 1 feeder once a week should be just fine
Yup, you may want to change to a 5 gallon glass tank or something similar, since it will be very difficult to add enough substrate to keep the tarantula safe from falls.