What is a "finger system"?

That's the septic.

I'm sure that you'd want to use the well water and also hook up to the septic, so right there smack in the middle of your driveway at the rear would be the easiest way to access both temporarily. I'd do the barn first, for storage, and carry the driveway paving to it so that you could pull up enough to unload building materials into the barn to keep them dry. Yes, the trailer will be in the way during construction, but it's the only logical site that's midway between the well and the septic.

I first thought the end of the driveway but was worried about being in the way. So you think that wouldn't be too much in the way Holly?

I thought that might be the septic system, but wanted to verify. My thought process was the same as hollysprings' between the septic and the well. Of course you will have to take your mandatory set-backs into consideration.

I would also do the barn first. But if you aren't doing the barn first, you could put the trailer on the barn site.

Yes, the plan is doing the barn first. What is a mandatory set back? I'm not aware of our county having that.

So that you don't have contamination issues, the house/trailer, well and septic have to be certain distances apart from each other.

I also suggest digging the well first. When we dug our well, the first hole was dry, so we had to have a second one dug. Placement of the well can effect placement of the septic and the house.