Stock My Tank!!!

First, keep some of your friends gravel - just half a cup will do. Keep that in the tank and keep the tank running and full of water. This will eaither eliminate the need for a cycle, or greatly shorten it. I've found that when setting up a new tank, adding gravel, rocks, etc from an established tank can lower the cycling time to about 3 days. I've done it 4 times. Also, feed the tank so you keep suppling everything with Ammonia and none of the bacteria die off. Don't clean up the food at first, let it decompose for a few days and produce ammonia. You can also add a dash of clear ammonia every few days.

Before you decide on a substrate, you first need to decide about what kind of fish you want.

Cichlids? Community tank?

On the sand--you can have it in a FW tank, but you'll want to understand how to take care of it. Sand can compact and form anaerobic pockets, where bacteria thrive, breaking nitrates down. These areas, if left alone, are fine, even helpful. If disturbed, they can release toxins that can kill fish. This means you either must distrub the sand regularly, or not at all. Some fish will root through and dig in the sand, while others will never touch it. know before you get into it, and maintain as needed.

There are different kinds of sand out there. The live sand sold at many stores and online is for SW systems--not for use in FW, unless your building a hard water tank for certain cichlids. There are also sands of different composition. Silica sand is inert, and won't alter the chemistry of your water, while aragonite and calcium type sands will raise pH, and alter hardness.

If you are getting the filter from your friends tank, keep the media wet during the move, and you should be good to go in adding fish right away. Do not let the tank sit empty for a long time (4+ days) or the bacteria will starve and die. Don't start cramming fish in, but stock slowly, a few every week or so, and test the water regularly to head off any ammonia spikes that might develop.

I'd make a plan first--know what you want, build the community on paper before getting wet. If this means the tank gets setup with no fish, buy a bottle of ammonia. Check out the threads here on fishless cycling, and use that method to keep the bacteria viable.

Rather than cycling with fish, check the threads here for advice on cycling fishlessly. With the kickstart from the established media and gravel, it should only take a little while, not damage any fish, and avoid the old "What do I do with these fish I didn't really want but cycled with?" issue.

As for long term--what kind of fish do you like? Do you want an active tank, or one that's more sedate? Biotope? Breeding fish? Lots of choices. First, test your water, and see what fish will do best in your current conditions. pH, GH, KH, temperature will all be important. Not that it restricts you, as fish can adapt to a range of water condition, but if you have really high pH and rock hard water, tetras will be trickier than say african cichlids.

Don't worry too much about the cloudy water. It will clear in time. If you want, you can add a floculant to speed clearing. Add ammonia and test until it reaches 5 ppm and hold it there until nitrites peak, then settle to zero. Do you know what kind of ammonia to get?