1. First, understand the Nitrogen Cycle. A tank needs to be cycled before it can really be stocked and safe for fish. Check out Fishgeeks.com
NOTE: If you do not follow the cycle properly then your fish will suffer and/or die. There are two types of cycling: Fishless and With Fish. I tried fishless unsuccessfully. What has ended up working for me was just getting a very few hardy fish and - the BIG key - adding BioSpira. BioSpira is not as easy to find but I know where to get it if you need. Marineland BioSpira is amazing in speeding up the natural cycle in your tank by introducing lots of good bacteria. BioSpira is kept in a refridgerator and has an expiration date. There's real critters in that bag! With BioSpira, I have had a tank cycle in a week as opposed to months!
2. How many fish to add? Definately start small and definately do your research as to what fish can go with other fish. Brackish fish need different water parameters than freshwater, etc. The rule of thumb to maxing out your tank with fish is to add an inch of fish per gallon, then leave a little extra. BE AWARE: Many fish you will buy may only be an inch or less but within a year then they could grow to be a foot long! Don't buy a fish without preparing for it's growth.
3. Equipment I have found to be unusually reliable:
1. Heaters: Marineland
2. Filters: Marineland Bio-Wheels
4. Chemicals I have found to be helpful:
1. NitraZorb is GREAT for high Nitrates (keep an eye on your pH when using).
2. BioSpira
3. Amquel & NovAqua
4. Aquarium salt when necessary.
5. Aquarisol when necessary