Makes sense. I have to do the same with my old Dixie Chopper. I smoke belts routinely but it's better than paying someone. I tried to cut half of my 50" cut today and burnt another belt. I'm so tough on that old girl but she keeps on cutting
As for 48" or 60" - It depends on how thick you are cutting, but I would be looking for a 60" because if the grass is too thick, just move over and use only 48" of the 60" mower. You don't have to use the whole mower!!! I only cut all of my fields in the dead of winter, otherwise, I just cut trails through the pasture.
I'm sure the tensioner could be better adjusted. I just absolutely abuse it. Years ago I had a Toro rider and took it to the dealer for some adjustments. He was pissed to find a palm frond boot up in the deck and said I needed to rake my entire yard before cutting. I told him to get bent and bought a used DC. Palm branches are tough to cut and even tougher on chain saws. If you cut down a 50' tree and cut it into 5' sections for removal, the chain WILL need sharpening. Oh, the cost of nice weather...