Uv Light

good morning all.
well here is the start of me proably asking alot of questions over the next few days as i try to work everything out in the new tank.

first question is the tank has come with plenty of gravel but althow it is fairly small and fine it feels sharp and scratchy in my hands and as i already know i would like some bottom feeding fish i will change to some sand or much smoother gravel but i was wondering would it be ok to use the existing gravel to form a bottom layer then add a layer of sand over the top there saveing me haveing to buy so much sand , or would i be better of replaceing it all with sand.

2 nd question is the tank has also come with a large external uv filter light.i havent seen much written about them here and was wondering what peoples general opinion of them are.
would it be worth me to plum it all in now from the start or is it something to look at in a later date when iam more settled with everything alse and have a slight bit of knowlage of what iam doing.
 (sorry about any incorrect spelling or grammar in my posts , one of these days iam might learn proper written english )

i am planning to have a few small plants dotted around to start with nothing to serious.
i have been thinking been thinking alot about the soil base (still feel sligthly nervous to put soil in tank ).
if i did use soil bottom layer is common garden soil ok to use i have a area to the bottom of my garden were i know chemicals have not been used for anything there.

I've used soil in all my tanks without problem, straight from my garden. Just check for worms or whatever so that they don't die and decay in it. There is no danger of "disease" from soil. Fish diseases pass from fish to fish, as there are no fish in the soil there is no possibility of there being any fish diseases!! Soil is mainly used if you want to grow a decent number of plants, I'm not sure if it is a good idea if you only want a few, though a few will grow and spread well if you choose the right ones. I'm biased in favour of plants, but I have to say that most people like the look of well-planted tanks when they see them. Don't put more than an inch of soil in the bottom, cover it with another inch or so of substrate. I put gravel on top of the soil, then sand on top of the gravel. I buy "J Arthur Bower's Horticultural grade lime-free silver sand" from the garden centre, far cheaper than "aquarium" sand and just as good, in fact it's probably exactly the same stuff. It's £4 for 25kg at my local garden centre.