I did that conversion. I tried buying bits and pieces and fitting it all together. I might have been better off if I had bought a kit from Hobie or Murray's. So that's my suggestion for the hardware side of things - unless someone pops up and says they have all or most of the bits.
The second bit you need is the sail - not included in the kit. Readily available, a window is good, a furling system is good too. Some boats with furling headsails have a zippered luff to keep things tidy up front.
I was also advised to upgrade my mast tang to cater for the extra loads.
Overall cost? I think Murrays kit is ~$1100, jib ~$300 and other stuff say $200. Sometimes whole boats are sold for that total, and that might also be an option if it happens to have the bits you want
Lastly trawl through the topics in the H17 forum, there is lots of stuff to read about the conversion.