being you have read my replies is hepfull to make this.

how I would do?

if you have a powerfull alt able to feed everything iddling, you won't have any problem to keep the ammeter working, even if is still the stock 40 amps alt.

A low charge alt won't ever suck enough power to get a full load charge reading at regular RPMs. And if does, will be for a minute or so.

but if your source everything from batt side keeping the ammeter, you'll have mostly sure a "ghosty" charge reading wich is not really a charge job, but really a sourcing job for the newer accesories. Is then, an unnecesary stress and load for the charge system, meaning this, wiring, terminals, ammeter.

The ONLY moment you should worried keeping the ammeter and sourcing everything from alt side is if alternator says byebye, or if you turn off the engine and keeps sourcing the devices/accesories somehow... i.e. fans relay being sourced from a constant power source instead keyed, but if this is the case, these will turn off by itself once engine gets cold, which should be more less quick.

the question is... do you want to keep the ammeter or not ?

myself, I wouldn't get worried as in fact really do. I have 6 relays sourcing my car with stock in everything but just halogen headlights, my 40 amps stock ammeter working, and stock 80's mopar replacement alt. All relays sourced from alt side straight from ammeter stud ( all relays inside the cab to be hidden making a cleaner engine bay view without splices anywhere ). Well of course, these 6 relays will be never working together, just 3 max, but normally 2, if I turn A/C in low speed and headlights. If turn on A/C on mid or high, 3 relays, since low speed is allways activated no matter the speed when you trun on the A/C( factory design on 70s Mopars ), but still just 2 getting the load.

next question... have you calculated how many amperes you'll need to source everything, and how much amps gives the alt iddling ?

THIS is the main to be answered... after this, you can decide which way to go.