I can't think of any reason why you couldn't put a new septic tank in. You will need to check in with your local Board of Health regarding any restrictions that might be factored in now as regulations in this area frequently change.
Best of luck to you.
But I also can't imagine why you'd want to:
Just like Tankless water heaters; the technology has come a long way in 20-30 years; there must be better way to do it now.
I envy you being able to statr from the ground up.
Good luck and may God bless