There are quite a few species of tetra and rasbora that are hardy
Personally i would rate both neons and cardinals as equally difficult to keep, cardinals are tempermental and need very soft water and slightly higher temperatures, neons are just tempermental and need a very mature tank and cooler temperatures than cardinals.
I would start off the tank with your Harlequin Rasbora as they are going to be your hardiest fish! Then some other hardy but pretty fish to consider are Black Neon Tetras and the Albino variation (lot hardier than normal neons!), Ember Tetras, Glowlight Tetras (very nippy though!), Zebra Danios (can be pretty aggressive and chase a lot!) Leopard, Glowlight, Pearl, Hikari and Panther Danios, White Cloud Mountain Minnows are stunning and with colour as a shoal! Cherry barbs would be perfect too!
If you want something interesting, you can always vary your kribs, a pair of nigerian reds or i really like the albinos! I have a pair in a 200L tank (it is very heavily stocked but also very heavily planted with a very mature 405 filter on it) but that pair is in with a pair of Stiphodon Elegans? Gobies, Large shoal of Cardinals, Shoal of Chela Dadyburjori or orange finned hatchets (these would be perfect in your tank! tightly shoaling and shoal higher up in the tank, yellow with neon blue stripe and spots down side, look like a danio) a small shoal of Cherry Barbs, a Small shoal of Pentazona Barbs, Albino Long Finned Ancistrus, an L no plec (mega clown pleco, wont get so big) some Amano Plant Shrimp (i'd avoid small shrimp as my kribs now they are big have eaten the red crystal shrimp! but not touched rock shrimp, amanos or pinochio shrimp) and there is also a big siamese fighter, admittedly he is a bit of an ugly chap be he had an attitude and a half, he was battering mollies 3 times his size and he will deal with the kribs too when he needs to, its just a case of finding an aggressive male not a wussy male!
I have to say, the cardinals and the chela dadyburjori look amazing together, the cardinals shoaling through the plant and wood level together and the chela shoaling tightly above them, now they are all settled to do shoal tightly, though i do have about 20 cardinals and 10 chela.
Just giving you some ideas
I would maybe add rasbora/danio/hardy tetra first and second, then the kribs third and if you go for either neons or cardinals, make sure the tank has been running with fish in it for 2-3 months before adding them, that way the tank will be nice and mature and less likely to fluctuate.
