Yes legally newly installed septic tanks need to be registered and a permit is needed to install the septic tank.
If you install the septic tank without a permit and it's found out eventually then you can get fined and have to dig the septic tank up and redo everything.
You also need a perc test of the soil to determine if the soil can absorb the water that comes out of the septic tank fast enough.
The permit and perc test is easy to get and do and actually it's likely cheaper and easier to have a pro install the septic tank for you.
The professional septic tank installer can get the permits and have the perc test done and then install the septic tank which would save you a lot of hassle.
Depending on the size of the septic tank it can cost from $3,000.00 to $10,000.00 for the septic tank installation when done professionally.