Check the Classifieds here if none put up a wanted ad and get some Java Moss.
Cholla wood is nice too, sometimes available in the Reptile area, just soak it in a container of water with Prime water conditioner and change the water a few times like once a week maybe soak for 3-4 weeks, if it still floats, that is okay, it will eventually sink. By then the shrimp will likely have something to munch on.
The Embers will get bigger, thicker not really much longer than the aforementioned
*Phoenix Rasbora aka Boraras Merah or Boraras *urophthalmoides aka Least Rasbora, Exclamation Point Rasbora, Sparrow Rasbora and the
*Boraras maculata aka Dwarf or Spotted Rasbora, or
*Chili aka Boraras Brigittae and the other almost forgot
* Strawberry Rasbora aka Naevus Rasbora
6 of them try - if you like best minimum a 5G cycled tank.
Betta will likely kill/eat shrimp, sometimes all is well and then bam! all torn apart and dead. I would for sure have a ceramic cave or Cholla wood and lots of moss and plants to give the little shrimp a chance.
Keep up on the pwc for best results. Not sure how good your filtration will be.
Get tiny food, Hikari Micro Pellets / Bites. They could starve if the food isn't tiny enough. Vinegar eels would also be a good live food.
Best bet would be 3.5G for Shrimp.
There is just a little more info in case you go bigger.
For the nano fish;
This helps figure it out. No matter what the lfs says - if they have these patterns they will be the fish stated. Not necessarily what the lfs says. They will not develope other pattern to be the fish you want, usually the Chilis. Only the Chilis get that red and only the dominate male and won't always be that dark cherry blood red only when trying to breed.
I would still recommend a larger tank. How about a 6.6G Fluval Edge tank? That is really a challenge to work in, lol.
Which boraras do you really have? A pictorial guide to the most common species | Invertebrates by Msjinkzd