With an AP you don't need gauges. Cobb provides a very safe tune. Read the notes for the map you want to run, make sure you have exactly what you can and cannot have and get the AP.
Stage 1. AP only. Flash Stage 1 map and you're good. Nothing else will work.
Stage 2. Full TBE and AP. Flash Stage 2 base map and you're good. Sometimes with the maps you can have the uppipe.
If all you plan on doing is stage 2, get the AP, get the TBE and Uppipe if you want it and call it good.
A good boost gauge is good to have but the AP has a realtime one built in. You won't need anything else.