I'm Toying with HOK myself, I bagged ten 1 oz bottles off ebay only last week. I do have some urethane paint by Inspire but as they stink I haven't been able to spray them yet. There are loads of colours and I am not too sure what to get either. I just grabbed a few different colours to have a mess around with it.
They guy at my local paint shop said they were great, but there are loads of colours and they are double expensive compared to other brands, so I think I am going to buy other brand base colours and use HOK for any special effects needed. I can't tell you what colours to get though. I'm hoping that someone else can answer your question better and give me info at the same time..
On another note, I've also been getting some pearl, holo flake and candy pigment powder to mix with my paints ( not just the HOK ) to get other effects. It's quite cheap really, I got 5 grams of candy red for £5 gbp that mixes with 100ml of 2k thinners and then can colour up to 1 litre of intercoat clear to make the candy at full strength. Pearl cost me £3.50 and comes in 25g so just under 1 oz in weight, I think that goes into 1L too. It's all for experimenting so good fun.
Lee