Don't feel bad, we all where there at one point in time, if it makes you feel better I have 7 freshwater tanks running all of them healthy but got 1(ick and another danio going curved spine again =<) , I'm setting up a saltwater tank now and I'm so lost and learning fish tanks all over again.
Just take a deep breath, your doing the tight thing, asking questions, wanting to learn, trying to give your little fish pals the best you can.
Check out Craigslist?,You could probably find a really nice cheap big tank I there, just be sure to inspect it ask for pics, or go in person, ask for them to fill it. I just got a 100g cube for 80 bucks with a stand filter god lights etc. it check out yard sales too
Just hang in there your doing great =)