So if you are wondering HOW many NEONS and/or CARDINAL Tetras you can fit into a 33 US gallons tank, then I would go with from 25-30. It seems reasonable to me mainly because I have that many in my 33 gallon already, but if you are a beginner then I wouldn't recommend you to put in that many. I put in that many because I do a lot of aquarium maintenance mainly every half a week (3.5 days) I guess you could say that :P
So if you are just starting to begin with neons and cardinals, then you can start with 15-20. It is what I started off with when I first started raising cardinals. The local pet store had like deals. Like 12 for so many ¥ so it was a great deal for me

Although I just moved back to Japan again from Canada, and then I just did a new restart for my tank that I bought and then I just started fresh, and within a few days (I used
RO water) the tank was ready. Heated, filtered, and plants already inhabited it.
Cardinals have more of a better chance of surviving. Mainly because the survival rate of Cardinal tetras are higher than the Neons. Why? It's because I hear that they are more immune to fish diseases than many other fishes. The hardiest of them all I believe is the Common pleco in the Western World. The hardiest fish in the Eastern World (China, Africa, india, Japan) could be the African Cichlids of Lake Malawi.
Although I haven't raised African Cichlids a lot. I just put them in my 10 gallon tank when they were small babies, and then I let them grow up, and then my friend took them and added them to his 2,500 US gallon tank fulll of large cichlids. But I never see him anymore so I can't tell you much more
Just on the phone xD
So anyways. If you like Neons then sure! You can go with neon tetras, but if you go with neons, then try to keep the water sparkling clean. like at least siphon the tank once a week. I do more than that but that's just me. Everyone has different methods of tank maintenance. Also, Cardinal tetras are more hardier, but they still like clean water too!
If you want to know what types of fishes can be adaptable with these cardinals and neons, then the types are:
Other community tetras, and angels (if introduced after ALL of your other fishes have been chosen) because angelfish when introduced first will claim their territory in the entire tank, and then they will give a hard time to the newcomer fishes.