The seceret building on a hillside is to not build on any loose dirt. It is extremly dificult to compact soil that is on a slope and expect it to last or support a structure. This is VERY expensive engineering and construction. You need to dig away the dirt to create your pad.
It's not the pad that will be all the work, it's removeing enough of the hillside to creat a drainage ditch that will keep the water from coming off of the hill and into your building that will be what gets you.
A big, wide ditch is the best thing for moving water. Idealy, you want it to move the water slowly and to be able to hold everything that is coming down the hill and off of the building.
The most common mistake is to quit too early and think it's good enough. If you don't build it for the 100 year storm, you will have massive damage and issues when it happens.
What you will see others doing is to dug an ugly, but deep ditch to catch water, or build a wall that never lasts to divert the water, or put in a french drain with the hope that it will accomplish it. I don't like french drains on the best of conditions. They don't handle very much water and they have a life of about a decade before they silt in and stop working.
Yes, that sized tractor will get the job done. The real question is will you spend the hours that it will take to do it and haul off the dirt?
Eddie