I've got 40 plumeria cuttings started in 2 gal pots. Location South Texas. These pots are plastic, and i put a little drainage rock on the bottom. The medium is 50/50 spaghnum peat moss and perlite. Perlite is very expensive where i am. So the first question is this: is the perlite really necessary? After 3 weeks nearly every one is sprouting leaves. Also, there isnt the proper nutrients to sustain growth in this medium. At what point do i need to put them into pots that has some sort of potting soil in it? I have some bags of Kellogs' potting soil. Its not very sandy. Should i add sand to it? And what about giving a little fertilizer when they are sprouting leaves? I have some Espoma organic fertilizer....maybe a teaspoon per cutting? More? Last, it seems to be the standard practice that you top the pot soil with a layer of pea gravel. Is this really necessary? One downside to this is that its harder to determine what the moisture level of the soil is when covered with pea gravel. Thanks for your advice.

Perlite provides drainage which is essential.
Do not top the pot with pea gravel. This is an idea that started many years ago and it seems that most people end up at the site which gives that suggestion.
Provide a very well draining mix (you can mix up to 50% perlite with the potting soil, and as soon as you have true leaf growth you may fertilize.
I would think that in South Texas you can put them in the ground? What are your winter conditions?

Its much too cold in winter here as the lows get down as low as 25 deg. Have to move all of them into garage with heater going on cold nights i guess. So i might be better off not adding sphagnum peat moss? Using 50/50 Kellogs' organic potting soil and Perlite from the start?

I would think (I have no experience with this) that the sphagnum moss will keep in moisture, you want to avoid that!

I would skip the sphagnum moss too. Too much moisture retention.