IDM is the injector drive module which opens up and fires the injectors, you can get it modded to keep the injectors open longer and have them fire faster giving a little more power and faster start ups.
Stages for injectors are the sizes. Stage 1 is 160cc with a stock nozzle, stage 2 is 160cc with upgraded nozzle. Stage 3 can be different size hybrid injectors or not hybrid
HPOP is high pressure oil pump and stock on an OBS and early 99 is 15* 99.5-03 is 17* and can flow more oil pressure to keep up with the bigger injectors
I did all the mods myself
Modded IDM ranges from 100-200 bucks or if your good with soldering and resistors you can do it yourself for basically nothing.
HPOP you can get out of a superduty that has one that is being parted out or whatever