Here in NC, you need a local Health Department permit and inspection for a septic system built to state specs. Each system is custom-designed for A. the specific soil type (determined by hand-bored random samples) and B. the number of bedrooms (1.5 people per bedroom - don't ask). The minimum size lot for a septic system in most NC counties is 20,000 sq. ft. (100' X 200' or almost a half-acre).
The number and length of leach lines is determined by the above and the configuration of the lot.
A basic minimum (good sandy soil) 3-4 bedroom system here consists of a 1,000-gallon septic tank, a distribution box and 210' of total leach lines (usually three 70' lines), and runs about $1,800-$2,000.
In addition to the drain field for the line layout required for the particular system, a duplicate area for a future replacement drainfield called the "repair area" has to be dedicated on the permit map and on the lot as well. A basic septic system, including the drainfield repair area, will take about a third of an acre. Just like the functioning drainfield, the repair area is not supposed to be driven over or built over (compaction and access).
After much experimentation, the septic system experts at NC State University have determined that the only "maintenance" needed for a typical gravity-flow system is to pump the tank at least every five years, and that all of those septic tank additives are worthless. Normal usage will provide ample adequate bacteria to make a system function properly.
We've been on a septic system for about 30 years, and I have the tank pumped out every year ending in a 5 or 0. No problems. The only other thing that I do, since our yard is so heavily planted with shrubbery and trees, is to flush a cup or so of copper sulphate crystals down about 3 times a year to keep roots out of the drainfield lines.
I don't consider septic system construction a DIY job. The last thing that I want is a faulty septic system backing up all of the time. LOL.
Mike