If I understand correctly, you want a very manuverable tractor to get into tight areas with a 38"-42" mowing deck AND it has to be able to operate a loader? Hmmmmm..... I'm thinking the Deere 400 series tractor is gonna be too big for the mowing job, but an excellent machine for the loader. Someplace you are gonna have to compromise one of the functions. I'm thinking since the mowing is the primary job, a smaller Deere, or a 2500 series Cub Cadet could be had with a smaller mower deck, and bagging system and adding an aftermarket
"Johnny Bucket" to the front. The Johnny Bucket is not a fulll function loader but a scoop bucket that will dig and carry loose materials, but has no high lift capability. That kind of set up would focus on mowing and bagging and compromise the loader part of your plan.