We got a new furnace and AC a year and a half ago, nice to not have to worry about the furnace, the one we replaced was from the 80's
Good to check reviews for furnace companies and get some quotes, the ones we got were all quite different
Use a 4 inch filter with a MERV 11 rating, it's pretty dirty after 6 months.
Went without a humidifier installed (they are apparently easy to add after if you really want) and put a portable one in the bedroom