how close are your customers from your shop? if you customers are all within maybe 10 miles of the shop, a smaller 200gal would be ok to start(close to shop for refills w/o alot of driving time) if your going to be hitting several large properties that require alot of spraying then go all out and get a 600gal unit. i use a 740gal tank w/ hypro D50 and 8hp honda 3/4x200' hose and spray @ 250-300psi and can spray about 50'-60'. i have 4 commercial prop. that i have to drive back to the shop 3 times to refill, there are alot of large pine trees (they seem to use more chemical then any). if you can't afford to go big like that, you can use your 200gal unit and fill from a fire hydrant. this is pretty cheap. around my town it cost $20 month for the meter and about $1.50 per 750gal. the only prob i ran into was i was filling up 1 day and was stopped by the water police in the what i thought was the neiboring town, opps, wrong side of the street. i just let him chew me out and he let me go.