Hello and welcome to the forum
Now, I'm going to be the bearer of bad news here.
I would not stock any neons or cardinals in a newly set up tank. For a number of reasons really, the neon tetras do not tend to do very well in new set ups, pretty prone to getting diseases easily, they do much better in larger groups in a larger established tank despite their small size, they are fairly active little fish. Stunning little fish display in a large group in a big tank thats set up with lots of plants etc.
Neon Tetra
Otos, again, they need an established tank to fare well. Especially need the bacterial film or algae to feed on, they can be difficult to feed, especially wild caught otos really. And a 64 litre tank is a little on the small side for a nice group of at least 6 really but its possible as long as is a well established tank.
Otocinclus
The Betta splenden is best kept singly in their own tank as they can be territorial / aggressive to tankmates. In fact they do best in tanks of their own of between 5 - 10 gallons (20 - 40 litres) with perhaps some snails and shrimps if they tolerate them (a gamble as shrimps are seen as food..... )
The most important thing to know BEFORE getting any fish is to know if your water is soft or hard, meaning knowing what your local water hardness levels are, which can be found online on your local water authority water quaility website.
For example, neons and otos are soft water fish and won't do well in hard water and other fish such as some species of rasboras and rainbowfish are hard water fish and won't fare well in soft water long term so its fairly important you find this out beforehand.
AND lastly, this may be obvious but have to ask, is the tank cycled? meaning have you set up the tank to be ready with the good bacterias thats needed to deal with the ammonia bioloads that any livestock will produce 24/7, ammonia is toxic to livestock so bacteria is needed to diminish the ammonia levels in a very brief nutshell explaination.
A lot more info and how to cycle a aqaurium can be found here -
Cycling Your New Fresh Water Tank: Read This First!