I live in Volusia County, and have installed 3 systems- 2 gravity and one pumped system. Twice I've used perf piep and once I have used infiltrators (clam shells) Here in FL, Septic permits are obtained in each County Health Department, then in the city or county once you have a health department permit.
A couple of things to consider from my experience I can share with you.
Its very very hard to DIY legally. Not impossible, but no one makes it easy. The State Health Department wants everyone to use a State licensed Plumber who practices Septic work as their business. Tanks and drain/leach filed pipe is going to be very hard to source. Distributors will not sell infiltrators to DIY, so you would be left with perforated corrugated pipe and sock, which is okay, and you can buy it at HD or Lowes.
I see a few hitches in your desires?
You might get denied a permit, if you don't have a building permit for the dwelling. How could they be sure you are sized correctly? Or sited properly?
You may need to consider the future. A bank or mortgage company, particularly if a "home inspection" is done to sell the house at a later date, think of your heirs, no record of a permit to install a septic system is a simple thing for a bank to find and will kill a deal.
The work is easy if the water table is low. If not, its a real chore. On the pump system I had to install a pump tank a few feet away from the existing single box that was concrete, 4wx5dx10l, and just below grade and just outside the back patio slab. The outlet from the original tank is the constraint. It had to gravity feed the plastic pump tank, where the pump would sit on a pedestal in the tank and when the float triggers, pumps about 100 gallons and shuts off, leaving about 40 gallons (needs to keep some weight in the tank so it doesn't float out of the ground). The main tank keeps solids and a "mat" of floating solids in it, and only really gravity feeds clarified water to the pump tank- similar to a two chamber tank.
I rented a small trackhoe to dig the hole, had to run a small pump to keep ahead of the water table filling it, and drop in and "sink" the plastic tank- because empty, it wanted to float in the constantly collecting groundwater in my hole. I had to over dig a couple of times to get the tank to sit and stay at the elevation I needed it. The round plastic tank looked kind of like a large grenade, and targeting the flat spot provided to get the 4" crossover pipe in the right spot, and have the manhole (to service the pump or pump out the tank if needed) at the right heights, was tough. I had to roll it into the hole, easy enough not realy heavy, and then push/hold it down with the excavator bucket while filling it with water to weigh it down so I could use my skidsteer to backfill enough dirt to hold it down on its own, then in the wet dirt, make the pipe connections between the two tanks. Not fun.
After all i just typed, the real offering was- you may not be able to build a septic DIY or otherwise, without a dwelling plan to permit. You also may be taking a risk with mortgagability on a DITY system here in Florida.
