Agree completely with SlimShadie concerning Femco. Good stuff and highly responsive customer service. Picked my similar rig up at Tractor Supply end of season sale for not much.
Made a frame bolts on top of brushhog over gearbox and cable-tied a receiver hitch cargo basket to frame. Tank sits in basket. Easy transport, stable, can use each independently.
For the driveway sealer you'll need a brass gear pump driven by your PTO. That's if it's a true sealer with high solids content. If it's more of an oil-type 'rejuvinator'-product you might get by with a plastic roller PTO pump. I think any of the 'sealer'-type products will quickly kill any 12-v pump.
Curious how you choose to proceed and your resulting experiences. Please post back so we may all learn.