5 foot will be the max and then that depends on how heavy aND how many and what size disks. But assuming a very light say like Howse model you probably will have to control the depth or else it will han you up.
My LMC disk is about 4.5ft wide and has I think it's 12 disks 16" in diameter. And when there cutting and buried up to the axles it's all my tractor wants.
MAYBE could pull Disc Harrow with 16" diameter pans for Secondary Tillage; i.e.: leveling plow furrows or working a kitchen garden annually. Implement only as wide as outside-to-outside tire width.
OP says soft ground, so draft force will be high.
DH1048: http://www.landpride.com/ari/attach/lp/public/specs/322-013s.pdf
Tractor does not have enough weight nor horsepower to pull a Disc Harrow for Primary Tillage; i.e.: breaking ground.
Primary Tillage requires pans of 22" diameter or greater.
Better to shop for a PTO powered roto-tiller.
Roto-Tillers and Disc Harrows are both soil mixing and smoothing equipments.