I use my Kubota L4610 with 39pto hp for making money, as a side job like you stated. From biggest income producer to least, I use a PTO stumpgrinder, Harley Rake, 6' heavy duty brush hog, 6"
chipper, and box blade. Along with these I always use the FEL grapple. I am ten times more efficient because of the grapple.
Most of my bigger jobs have been increasing the size of people's yards, so taking down the trees, grinding the stumps, chipping the wood, grading the area, and then power raking.
I get a lot of stumpgrinding jobs for just stumpgrinding, but the majority of them turn into some sort of additional work. (Like more clearing, or chipping a pile etc).
I turn down a lot more stumpgrinding jobs than I take. I pick and choose the jobs I want to do. I've paid for every implement I own by my side jobs and have made a fair amount of fun money as well.
My favorite jobs are pasture renovation, especially if there is 10 years of growth or so. This is hard on the tractor but it's so satisfying to see the end results.
Hope that answers your question and feel free to ask more, it's how we all keep learning. I'll be interested to see other peoples replies.k