Hm, about every two to three days is normally a good feeding regime for an adult frog. Yours is very small for its age, but I would try it like this. Just watch it carefully; you will soon find out the right amount.
I´m not sure if it will grow despite of it´s age or if the bloat will reduce (could be a permanent kidney damage amongst other possibilities), but there still is a good chance that it will have a good life with improved environmental conditions. High quality food might help as well.

As we don´t have Petco shops here, I can´t say anything about those plants. But many bacteria/ parasites will die off if you quarantine the plants in a bucket of water (with enough light and daily water changes) for 1-2 weeks before adding them to the tank.