A diesel would have other advantages as well. Much of the rental equipment on the market such as small excavators, small front end loaders, etc, use diesel engines. At some point as your business grows you may want to add a fuel tank in the bed to refuel those rentals, and running both the truck and the rentals off of the same fuel is more convenient.
Any truck used in a handyman business will probably be hauling sheetrock, lumber, tools, power equipment, joint compound, concrete mix, etc. etc. on a fairly routine basis. It'll probably be towing concrete mixers, trailers, etc. as well. It'll get beat up no matter what you buy. And, of course, you'll want a good professional sign on the doors. Your girlfriend may have to adapt.