The size of pot is fine.

I think you have a slight case of a Nitrogen deficiancy. Leaves are dying from the bottom up and brown spots it looks like.

I read that you have only fed it 4 times. I suggest feeding it again within the nest few days before all the leaves die. Just don't feed over the recommended amount as that will create a whole new set of problems.

The plant right now needs something high in Nitrogen (N-P-K). I use 5-1-1 Fish Emulsion (organic), but there are plenty of other choices out there. Just pick one that has a high N number compared to the rest. If your MG has that, then feed again.

Good luck.