Don't take this the wrong way, but I've seen this 100 times before. So you got everything you need to mow lawns, you think. The weak link is that tractor. It's slow, fragile and bound to become undependable. But you're in no hurry, you've only got a few accounts. You take your time and do a nice job and you start picking up more accounts. It's spring and the grass is growing like crazy, you're having a hard time cutting and not leaving clumps, it's taking you forever it seems...then it rains for a full week. You can't even get to last week's lawns let alone this week's lawns...the phone is ringing off the hook with customers wanting to know when you're coming and you don't know what to tell them. And then the tractor dies and they say it will be at least a week before they can fix it. Now what?
That tractor is made for cutting one lawn once or twice a week. You cannot depend on it to run a business!
Get a commercial walk behind mower even if it's a 36 inch belt drive.