My best advice is to look back at the last 100 or so jobs you did and write down what it encompassed. For example (finish grading a yard with Rake, pushing trees over, etc) Make note of the type of surface you run on for each job. Make note of all jobs you lost because your equipment was inadequate.
These things will help you decide between tracks and tires and also help with the size of teh machine. There is also excellent finincing on used equipment if you have good credit. As low as 4%.
I was in a similar situation as you. I had L3710 tractor with Harley rake that I was using. I felt that going wiith a skidsteer( like a JD318) in a smaller size was a lateral movement and felt that I neede to step up in size so I ended up with a TL140 and I have never had a situation where the machine was too big.