Welcome, and good luck.
And now, I begin!
First of all, you do not want a clown loach in this sized tank...they get very big. Most sites will list them at 6", which is already too big for your tank, and I've seen them MUCH bigger. If you go through the recent threads on here, you'll find a post on them that has a video linked, and you will see some monster clown loaches. They also like to be in small groups, and even if they grow to half size, you can't support a school in your tank.
Got a hunch your orange and black tetra is a serpaes, I bet. Is it a little bit testy? Like to bully other fish? that being said, tetras are schooling fish, and will "behave" better if kept in larger groups, say a minimum of 4-6 of a single species.
Read that article on the cycle. Buy a test kit. Read the article on the cycle again. I believe the test kit most reccomended here is the one that you've got on order. (where did you order from? what site? curious myself, living up north here, on where folks find stuff)
You might want to check out the "What should have a warning label thread"
http://www.aquariumadvice.com/viewtopic.php?t=91798
It will give you a good idea of what not to look for, and what you should be thinking of when you're planning your fish purchases. Get an idea of problems that are listed there, and when you're ready to buy more fish, research them and think if these problems apply.
Find out what species of pleco you have. If you don't know, post a picture here of it and someone will tell you how big it may get. You really should post a pic of your tank anyway, cause we all want to see your set up. I love to see everyones' idea of a great looking tank. Always gives me ideas for my own. Back to the pleco...depending on the species, they will grow and grow and grow and grow and grow...no, really, it will. Post pics of any fish that you have, and you will get a proper name quite promply. There's some great people here just waiting to spread their knowledge.
This is a generalization, it happened to me and I know of a few others who have spoken about it. I have found mollies to be very fragile and short lived. This is likely attributed to a large amount of inbreeding, so I've heard. I have never been able to keep one over a year, even in tanks with German Blue Rams, which are a very sensitive fish.
There are some sites that will give you community recomendations. One that I liked to use as a starting point was Elmers
http://www.elmersaquarium.com/ under their FW handbook section. I believe Drs. Foster and Smith have something similar.
I'm sorry if this comes across as all negative, but, well, it is. I really do welcome you, and hope you find the hobby very rewarding. Please post lots of updates on how you're doing, and feel free to add a photo or two. I learnt way too much from mistakes, and I try to pass on those things as much as I can...enjoy your tank, take care of your mollie babies (do you have a breeding tank so your fry don't get eaten?), and prepare for the onset of MTS soon. Ohhh, when it bites you...
You probably don't really need it yet, not with a 20g, but once you step up, get a Python for doing your water changes. BTW, what is your current maintence routine? What conditioners do you use? Are you planted?
Out of curiosity, where abouts in Canada are you from?
Ha ha...that's enough out of me...
crap, I better get some sleep...so tired.
