In your private messages, is what I mean. When you go to reply, you should be able to delete whats already in the text box or make some room at the top/bottom by pressing the enter key a couple times. :)
Like a lot of hobbies, if you really want to get into it and do it right fish keeping takes a lot of effort, research, and money.....its really not as simple as putting a few fish in a tank and that being it. It is a lot of work. And especially since we're talking about the health and well-being of living creatures here, its even more important to try your best to learn and do things properly so you can have a successful setup with healthy, happy fish.
I'm very sorry that you feel like you're always wrong, that is not at all my intention or the intention of anyone her on the forum. We say what we say and offer up our advice based on our own research and experiences because we want both your fish to be happy and healthy, and for you to have a good experience keeping them that way.
To start off, cycling a tank is a lot more complicated then just setting it up and letting everything run and it can tank a good 4-8 weeks. Give these threads a read, they should explain things in much more/better detail then I could.
Unless you really want to get into larger species of fish(most of which could likely eat your bettas, mind, if you had wanted to add them in as well that is), then I don't see why you would HAVE to upgrade to a 55. Its great if you want to and you have to means to of course, but if not then why not just choose species that will fit in what you have? A 20 gallon is still a nice size. Can't put anything massive in there, but it does give you some nice options IMO.
Honestly, I would suggest putting anything in that will potentially outgrow your tank, especially when it comes to plecos or 'algea eaters'. Trying to keep a big fish in a small tank while its growing is not a good plan.....it can stunt their growth and cause all kinds of health problems that will pop up later on. Its best to stick with species that can really fit in your tank long-term, IMO.
Also, most plecos and algea eaters don't really eat algae at all/for very long anyway....and they produce a TON of waste, which will further limit your stocking options. As they get older, many species, like the CAE, can start to get rather aggressive as well and have been known to attack and suck the slime coats off of their tankmates.
But on a more positive note, you do have room in your 20 gallon for some smaller species of catfish, like Corys(or ottos, but they can be a little sensitive and finicky). You could easily fit in a little shoal of 5-6 corys to scurry about the bottom, even if you wanted to add a few more girls and start a Sorority. ;)