Generally it is best to wait until the end of the project to put in the septic field so that big trucks aren't driving over it. You will have to hire a licensed contractor for this step. Remember to get the access risers if the tank is buried deep. Also, remember to plan to have 2 20AMP circuits available for any pumps or warning systems associated with your onsite wastewater system. If you can afford to add a gray water system, that is very efficient way to have water for a landscaped area.
Your septic contractor may also move some more dirt around to fill in around the house. It is likely that a large amount of backfill material will be leftover from the septic field. I also love using scrap rock for backfill because it is stable and I usually get good landscape blocks inexpensively from the pile. You might also be able to get your septic contractor to touch up your road inexpensively since he already has his equipment onsite.
You still have a few things left to do, there always are. Once all the lights and plumbing fixtures are intact, you should be able to move in. You can hang wallpaper, install knobs and handles, add mirrors, and hang blinds as time allows. If you do hold back a little money from the paint crew, you should also be able to get them to do a touch up run to catch dings from the final stages of construction and move in.
Congratulations, and enjoy!!!