First of all welcome to the forum!!!!
Choosing a tank:
If you debating between a 55 and a 75 gallon tank...do your selves a favor and get the 75G....you will thank yourself for it in the long run. Besides the fact of being able to house more fish, landscaping for a 75 is a little easier than a 55 because you have some extra depth.
Most importantly, make sure you let your tank cycle....a fishless cycle, although patience is needed, it's well worth it, you can read up on that here: Fishless Cycling Made Easy
A great place to check for aquariums is Craiglist.com, you can find some amazing bargains on there, my brother just picked up a 100G tank with a stand for $125 bucks. Maybe then you could even go bigger!!!!!
Some other things you will definetly want to pick up for either size tank would be:
A good dechlorinator (Prime is a fantastic product)
Extra filter pads for your filters (you want to change your pads out maybe once a month, but NEVER change the wheels, thats where all the good stuff i!)
A gravel vac/siphon for water changes
Bigger Fish net
1 or two 5 gallon buckets for water changes
Gravel or a subtrate of your liking
plants(real or fake, real plants you will need to get into certain lighting needs)
A API Master Liquid Test kit (this will be the best $25 you spend on your tank, it will save you countless trips to your Local fish Store (LFS) and will last quite a while.
I'm sure there's some stuff I forgot....I've been at work since 6:00am.....
There are alot of options are far as filters...but, two of the best are Marineland Bio-Wheel and Emperors. For either a 55 or 75 tank you will want two (or a powerhead). Two (2) Marineland Bio-Wheel 350's or Emperor 200's will definetly do the trick. You could
get away with only 1 bigger filter, but some hobbiest say it leaves little filtration on the otherside of your tank.
Once your tank is established(aka, cycled) you will need to do weekly water changes of about 15-20%, that is standard for all tanks, so the only difference here is, is that the 75 will require just a little bit more work for your water changes.
All of those fish are great community fish, tetras should be kept in schools of atleast 6.....the best thing to do would be to take a trip to your LFS and write down some fish you like and the people on here can give you compatibility reccomendations.
Thats about all I got for right now, time to go home!!!!