A 16S15-14 can build 173 PSI. The pitless will see 1 PSI less than that for every 2.31' down to the static water level in the well. Use long insert or barb fittings with two hose clamps instead of compression couplings on poly. A 20 gallon size 202 tank is fine but is larger than you need when using a CSV1A valve. You can get that $179 CSV1A in a complete kit including a 4.5 gallons size tank for $395.00 total.
50' of rise after the pressure switch and tank will take 22 PSI. You might want to run a 60/80 pressure switch with the CSV1A set at 70 PSI to make up for the elevation rise. At 60/80 pressure you will need larger than the 4.5 gallon tank, so you can use the 10 gallon available with the kit for an extra 50 bucks or go ahead with the 20 gallon tank you were thinking of. You can also get the PK1ALT kit, which the LT means less tank, and attach whatever tank you want to the 3/4 port on the bottom of the CSV1A.
