Is the working pressure of the manifold you mentioned, the range I see in this picture? For example, the 250C has a range of 4-80psig and the 250D series has 5-125 psig.
I do not believe I mentioned a manifold; only the delivery pressures.
If my understanding is correct, a lower gauge that goes up to 100psi may work for both of these series since, for our purposes, we will never go past the 100psi?
In other words, can a 100psi lower gauge be installed on a 250D series or is a 200psi a best choice?
Yes, it can. You can leave the 200 PSI gauge on as well; I use a Victor that has a 200 PSI low pressure gauge and it increases in (minor) increments of 5 PSI and major increments of 20.
Calm down, most of us have work to do