I have started getting more and more requests for birthday/wedding cakes but am by no means professional! i really need to invest in a good quality piping set, ideally including several tips, 2-3 bags, a coupler and perhaps a flower nail.

I am actually doing a wedding in august and as well as the main cake, the bride has requested 100 cupcakes, 50 with purple swirled icing and 50 with silver swirled icing. So i'll need a good tip for that, and also need to start practising them! I tried a few cupcakes with that kind of icing before, but i think the kind of 'star' tip i had was too small, because i had to really squeeze hard to get the buttercream out and as a result the swirls were kind of squiggly!

So i would really appreciate any advice on the types of nozzles you use and where you bought them?

I use Wilton stuff. I bought a tackle-box style kit that came with supplies for the Wilton courses. It has several basic tips, couplers, a bag or two as well. Check out contents online. I have added many things but as far as a good start it was great. It was $40-$50 at Michaels and I used a 40% code. I needed all the stuff for the class anyways but I found it a decent value. Also check your local Goodwill, I found a brand new box of Wilton tips there for $1.99!