I haven't done a hard-top specifically but have done some spraying. If you are worried about it turning out shit, the question I would ask myself is "can I afford to do it again" because the worst that can happen is you mess up and you sand back to the start and do it again.
Also what were your plans to do it? Spray cans or proper gun? If you have a compressor already, get a gun and use proper 2 pack paints. Much harder wearing but they are more expensive. The expense on the 2 pack is with the extra ancilliaries like hardener, thinner, primers and laquers that you can usually only get per litre. I would expect you would only need 250ml of actual colour but if its your first time I'd go 500ml just to be sure. Its definitely better to be looking at it than looking for it. Expect to pay up to 150 for all the paints, thinners and gun by the time your done.
The finished product is going to depend very heavily on the time and effort put into prep. You can never over-prep for painting. Aim to allocate your time, 95% prep and 5% paint. The surface needs to be perfect before painting because any small imperfections in the surface will be magnified tenfold on the finished product. For painting you will want to have a straight run at it. Read the instructions specific to your paints and adhere by timelines exactly. Lacquer bubbling and peeling down the line is usually caused by allowing the colour coat to dry too much before applying the lacquer.
Read lots of material before starting and the more gen you can get from reputable sources the better. (i.e. forums are not always the most reputable sources of gen so from that point, even if you take nothing else from this post, take that!) Time and preperation are key so if you can afford to give the time and work to it, you will be rewarded. In my opinion, go for it.