OH MY GOSH GET GHOST SHRIMP THEY ARE THE COOLEST SHRIMP IN THE WORLD!!!
I used to have 3, but I gave one to my close friend, my fish ate the 2nd, and my 3rd is like a ninja, so I rarely see him.
But I keep my moss ball at the front of the tank, and just seeing Ash poke his little bitty claws into the moss to search for food is absolutely amazing.
And when they eat their food (algae discs or betta pellets. Betta pellets work just fine) you can see the food go down their throats, and into their stomachs. It's awesome! And also because they're see-through they look like little robots when they move, you can see all their joints and appendages....I've learned so much about shrimp just from my 3 ghosties.
Also Omelette was tailbiting from boredom, which is why I originally got my ghosties. With all the activity of the shrimp toodling around, Om completely stopped tailbiting.
If you want ghosties you'd better get lots of plants! For my 3 gallon I have one big foxtail plastic plant, and 4 other fake plants, and a Marimo Moss Ball and a tea cup that's Om's "bedroom". Ghost shrimp become food aggressive (only with their own species) and even though it's fun to watch them steal food from each other, it would be just plain mean to force them onto each other's territory all the time. Lots of live or fake plants (it doesn't matter) is the key to happy shrimp :)
Also you'll need an air pump for the shrimp to stay healthy. Not only will it be good for the shrimp, but your betta will love it (I make fine streams of bubbles and my Om loooooves to swim through them. He has a whole routine when he goes about this business). There's nothing special needed to acclimate.
Just do what you do with a fish!
You can safely fit 7 Ghost shrimp in your tank, and that will be lots of activity so your betta definitely won't tailbite from boredom.
It's easy to tell the difference between males and females, too. Females are a lot larger and have a big green spot somewhere in the middle of their body. Males are just clear and you can see a few tiny organs in the fronts of their bodies.
One last thing is that plants definitely are needed as hidey-holes because when shrimp molt, it's stressful and they need to be safe from your fish's prying jaws and other shrimp's picky claws. They like to molt in a secure place so try not to move the molting shrimp around too much while it's molting.