i'm a little late to the game on this one, since you've already got it planned out. my question was: do most of the small pad jobs you do allow you to use a ready-mix truck, or are you using a small mixer on site? if you are using a small mixer and were then going to move it by tractor, what about a 3ph pto mixer? i just brought home a slightly-past-abused 3 point hitch pto driven mixer. it needs a bunch of work, but they still make similar ones new if you are in business. with that you can back right up to the forms & place it where you want it. i don't know how bad the cost is compared to a bucket, but it would cut out a piece of equipment, and the transfer from mixer to tractor.
My tow behind concrete mixer has mostly been sitting. Not a lot of call for brickwork these days with this horrible economy. I thought of a 3pt mixer, but didn't want to mess with stone, water, portland, etc. It's just easier to pump it or shuttle it in on a concrete bucket.
The jobsite is like working on a 30* angle all day long. No place to sit a mixer. Mounted on a 3pt it might work (go up to level spot, mix batch, then drive up hill backwards and drop a load), but that would be kind of slow.