my new fish tank

Question
Hi, ive just set up a new fish tank but have not yet bought any fish because we have to let the water become safe for the fish to live in and then after a week we are taking a water sample in to a local aquarium to be tested for safeness. The tank is pretty big and deep but im not sure what size exactly... its has an under- gravel filter and a heater aswell. When it comes to choosing the fish we dont really know where to start so i could do with some help! I would like a silver shark but ive heard that they like to be in fours or fives.... my mother would like some of the small neon fish aswell so would they get eaten by bigger fish? And also if i were to get one of the axolotyls (mexican walking fish) what would they be compatible with? And last but not least we saw some bumble bee gobys which we would like but arent sure if they would get attacked by other members of the tank if we were to get different types of fish... please help and tell me what would be ideal for our new tank... if possible we want it to be nice and interesting with some different and unusual types of fish and some normal ones!!! Thankyou and i hope you can help me, x.

Answer
First off, you will need to figure out exactly what size tank you are dealing with, this needs to be done for many reasons, like knowing how many fish you can stock. Rule of thumb (in a well cycled tank, more on this later) is one inch of fish "per" gallon of water/tank size. I think this is a little off, I have slightly more than that in my tanks. Water changes are a necessity!!! Especially if you have more fish than the thumb rule. A cycling (more on this later) tanks water needs 25 percent changed every two days for about six weeks, (I prefer 8 weeks) an existing tank would need 25 percent changed weekly, a large established tank would be 25 percent changed monthly.

Second, you should let the tank set for more than one week. It actually takes at "least" six weeks (I prefer 8 weeks) to "cycle" a fishless tank. Here is a web site about cycling, http://faq.thekrib.com/begin-cycling.html
The beneficial bacteria takes a while to build up but there are a few ways to jump start this ...

You can start jump start the cycling process with a product called Cycle, (costs $5 - $6) always read and follow directions carefully on any chemical or additives labels, it will say treating NEW TANKS use two capfuls "per" 10 gallons every seven days for two weeks then switch to weekly maintenance/existing tanks. (it is a good idea to do this before adding even one fish)

Another way to jump start is with a cheaper hardy species of fish, but please stay away from the common goldfish unless that is "only" what you want in your tank. Here is an excellent page of fish species for cycling, some of these are not to cheap so you will have to check the prices, http://www.aquariumpros.com/articles/fishcyclefw.shtml  
but please remember to only start out with two inches of fish "per" 10 gallons of water/tank size. Then wait about twenty days - a month before adding any more fish.

A third way, although I do not recommend this, other than with my own established tanks due to parasites and diseases, is to use the filter from a friends tank if they have the same type. Just buy them a replacement filter. You could even use the water they are changing as it would have the same effect. A handful of their gravel would do the same etc.

The heater should be set to around 78 degrees but no more than 80. Most of the Sharks I am familiar with also do require schools of five plus.
The Neon Tetras are great little fish. I have six of them right now and they are hilarious little clowns. They also prefer to be in shoals of five plus and are NOT good to start out the cycling with. After your tank gets going good, they would be fine. You also need to decide if you want bigger types or smaller types of fish due to the aggression and appetite of some species.
I would not recommend the Mexican Walking Fish as a community fish due to the fact that they require at least 20 gallons of tank per fish and they tend to get very aggressive. They will attack and eat tank mates or (if more than one) each others limbs if they get hungry and all fish seem to always be hungry so they are not compatible even amongst themselves. If you were to get these I would do a species only tank then and keep them very well fed.
The Bumble Bee Gobys will be fine as long as you don't over populate them, one per 10 gallon of water/tank size. They can be (not always) territorial with each other but normally are very peaceful to other species of tank mates so are a good community fish. Here is a good compatibility chart, http://www.ratemyfishtank.com/freshwater_compatibility_chart.php  this is no where near the full chart, just a more simple one. I still haven't found a full one. Maybe I'll start my own ... hmmmmm,  ok, but anyway at least this is a start for you.
Also you will need to provide lots of shelter and hiding places for your aquatic friends. Plants/ fake or live would be best (helps remove harmful toxins in the water), rock caves, DoItYourself pvc pipe caves > http://www.aquariumlife.net/projects/diy-decoration/99.asp  
You can also use the pvc elbows, just make sure you use big enough ones for the fish to have some room

I hope this is helpful for you. Send me a follow up if you have any more questions or problems.