Make sure the drainage doesn't sit in the bottom of the decorative outer pot. I don't grow these so I don't know how much water they like- "damp but not wet" sounds likely to be too damp though.

It's name now is Philodendron bipinnatifidum, the name P. selloum is from many years ago.

When you say "... lower, younger, smaller leaves yellowing", remember that when the plant is young the leaves are smaller. As it grows the new leaves become larger and are up top. So in fact, the smaller leaves are the oldest. It's not unusual for the oldest leaves to yellow and fall off. Repotting does stress plants and that can accelerate the yellowing. If the newer (bigger) leaves are looking okay there shouldn't be a problem. They can take a bit of drying out but if the leaves become limp then that's too dry. Generally though, they're fairly easy plants and quite 'forgiving'.