So I buy fish from a freshwater retailer, poke a couple holes in the bag with a needle, and set it in the water.

How long should I leave the bag in the water before it’s safe to let the fish out? A few of the fish I’m after are too delicate to go through hours of bucket dumping, and siphon dripping, so the bag/diffusion method seems the wisest choice. I’m assuming the time would depend on the salinity, I’m aiming to set the tank at 1.008, keep it at 81*. Salinity, hardness, pH, oxygen, all the other factors considered, how long should the fish sit in the bag before they’re released?

At this point, I’m just in the researching phase, any advice would be absolutely wonderful. Ideas, fish suggestions, tips, techniques… I haven’t had an aquarium in 4 years, so I’m a little rusty. I’ve only ever done freshwater, which seems considerably easier. I’ll be using sand as a substrate, intend on live plants, driftwood, and rock slabs. Outside of the brackish fish, what freshwater and marine fish can adjust to a brackish environment?

Don’t tell me about mollies, I already know. XD
Okay, I understand that ammonia among other things builds up inside the bag, but two cups of water in 150 gallons shouldn’t throw it out of whack. I never had a problem with that. Supposing I’m going to ignore that tidbit of advice for the time being (I’m starting with mollies, ghost shrimp, and, yes, guppies, so I highly doubt that little bit of ammonia would wipe them out. Especially when they spent the time IN the bag to make it that way). How long for the water to diffuse?