Are you planning on eventually growing the business past what you stated? no plowing/no 4x4, waste of gas/ possible repair, and cost of 4x4 is at least 1k more than not. honestly everything you stated, a compact truck can handle without being abused, you can always rent and abuse a home depot truck for a specific job. I've always been in business to make money, not for haveing the biggest truck... depends what your goals are. I would definitely go with a 6 cyl though. For the hauling, mulch doesn't way anything and top soil is heavy for a 1 ton truck also, just take two trips for the few times you do top soil, i don't think its worth the extra cost of a full size. Just my opinion.
2006 Isuzu Turbo Diesel Beaver tail
1990 3500 dully dump "The Roach"
2012 Scag cheetah 52"
2012 Scag Turf Tiger 61"
2008 Scag Turf Tiger 61"
2009 Scag Tiger cub 52"
1998 Exmark Lazer 48"
2 199? Scag hydro 48" walker Behinds
Bunch of blowers, and all the other necessities.