Go for it. Depending on which kit you're using, dry hopping with an aroma hop (like cascade) or a dual purpose hop (like Amarillo) will add aroma to your brew. Don't dry hop with a bittering hop (like pride of ringwood).
How much to dry hop? Again it depends on the kit. And on the alpha acid % of the hop.
Dry hopping was the first step towards ag for me. From memory it was a coopers draught kit with 1 kg dry malt extract, dry hopped with 20 or 30 g of cascade 4 days before bottling.
Have a look at the recipe data base and filter on K&K. There will likely be kits and bits recipes in there that will be a good start for you.