Never deal with hole in the head but we had oscars for years and it was a lot of work-I think the salt water was easier!
I'd look into a bigger tank now. It seemed any time we ever had an issue with the fish a bigger tank helped. It doesn't seem like they are too large but the extra room seems to keep them less stressed and in general able to heal or not get sick/injured in the first place.
Also make sure the filter you get can handle the tank-especially if you will soon be moving up to a bigger one.
We fed feeders but also gave pelleted feed(which some people seemed to think one or the other was better.
Honestly we used to use the over the back wal mart ones
Did fine. We didn't switch to canister filters until we got into saltwater. Now we have a 175(I think thats what it is!) with the penguin filters(again not positive-the fish is more the bfs area!).
What we seemed to have learned over the years is there are certain places you do and don't buy fish around here. The bfs cousin had horrible problems going to whoever was cheapest when he had the same set up as us if not better.
Our oscars were huge and we ended up giving them to the bfs cousin because the giant tank we had them in was just to much for the few fish we had in there. They were neat fish though. Now we have some smaller Cichlids, like yellow labs and some weird Chinese sucker fish things. Which we were given by a friend. I think we have all been passing the same fish back and forth for years
I hope you find something to work for you-Wish I had some specific advice. I do want to remind you a jack of all trades is a master of none-not getting into that argument but I do see a lot of advice given by some that seems to be pulled off a page and recited from somewhere.