I have a Case 1550 dozer and before that I rented a Deere 450G dozer. They are night and day different in size from each other, but I learned a few things from each of them. HP and weight make a huge difference when trying to move material, or break through the hard crust of the ground in summer. The 450 was just too small to clear the land or dig into the dirt. My neighbor had a guy with a D4 clear his fence line and that was also too small for what he was doing. Took him forever, and the piles he created are still there.
To build your track, I would think you would want as much HP as you could afford. To maintain it, smaller is better because you have more control for finish work. I would think something like the D5 in the low 100 hp range is going to give you the best of both worlds. The smaller ones, like the Komatsu, wont be very good at getting much done. They are more for the residential pad builder getting a lot ready for a house in some neighborhood.
Case has been rather poor at maintaining parts. I've had to contact salvage yards for mine on several occasions and pay ridiculous amounts for what I got. They also have a terrible policy of only supply entire units to fix a small broken part. When one of my hydraulic pumps stopped working, they wanted $25,000 for a replacement. They do not sell any parts for it, you have to buy the entire unit. Luckily the parts guys at New Holland told me where they get their pumps rebuilt and I was able to get it done for under $3,000
Cat is famous for having parts for everything they make. Deere is like Case and after awhile, stop carrying parts on some of their older models. Komatsu makes some great equipment, but they are high on their prices for parts. They also have a lot of grey market dozers out there that the US dealers do not have the parts for. I don't understand all that, but I've read enough comments on how hard it is to get parts for the grey market models to avoid them.
MachineryTrader.com | Backhoes for sale, skid steers, excavators, dozers. Equipment Trader | new and used Equipment for Sale | and don't forget Craigslist. Be careful of going to auctions. My Case dealer told me that's where they dump all their equipment that is too expansive to fix. It might start up and run long enough to fool a buyer, but it's too far gone to put the money into it that's needed.