It's a lovely little tank! Is this your first fish tank? Can tell you've been doing a lot of research and have put a lot of thought and care into it!
Endlers are fine with flow, I've always found that both guppies and Endlers seem to almost play in the output, especially after a filter clean when the flow gets stronger.
I'm a bit confused on the variety of species mentioned - Endler's and Pseudomugli (my pseudos don't look like they're upside down! Hmmff
) are hardwater fish, while CPD and thhe rasbora need softwater. Have you and
@Essjay figured out the GH and pH of your water yet? Especially if you're mixing water sources, might be worth investing in the API GH and KH test kit so you can make sure you're keeping them in the right range as you figure out the ratios for the different water sources.
If you're ever in the Bristol area, there are two big chain fish stores that I don't recommend, and two privately owned LFS. One is called Parkers, which I've never been to, so can't give an opinion on, except that they seemed nice on the phone and were willing to take in a rainbow shark I rescued if I couldn't find a home for it, which the two big chains wouldn't do.
The other private store I do highly recommend! Called simply 'The Fish Store' in Bedminster, Bristol.
It's not a huge store, but they've made the most of the space, with a lot of tanks, healthy and beautiful fish in a wide variety each time I've visited, and they've been fantastic. Lots of nice things in store in terms of tank/wood/decor/shrimp/plants, beautiful, planted display tanks, and lots of nano fish too, not tank busters. I've sung their praises in other threads. But if you want inspiration, guidance, or fish, I personally think they're great and worth a look around. Prices also more reasonable than the chain stores.