I have been regularly sailing various Hobie mirage kayaks for years now.
The loads on the components required for sailing these boats are so tiny and the materials so strong that there really is no point in oversizing any component or over-engineering anything you don't have to IMO. As a result you really don't need to do anything fancy schmancy to attach your blocks to the kayak - just tie them on with just a bit of light line: cheap as chips and totally removeable & replaceable.
As to the choice of cleat for the mainsheet, cam cleats are fine but they are pretty big and have moving parts. My personal preference is for a "cLamcleat" note the spelling & search the web for them) of the appropriate size with or without a shim and/or one of the various 'keepers' that are designed to work with them. (The style I use looks like CL203/CL211 and there are various options in terms of beckets, fairleads, keepers shims, etc - several configurations would work well but in my selection I have always been mindful of the need to be able to dump the sheet in a hurry). I would install my clamcleat under the bungee net of the RHS tray in a direct line with the lead of the sheet; this way you can have the cleat exposed for use or covered by pulling the net up or down over it... Works great.
Just one tip - if it ain't tied on you will lose it on your first capsize
Hope this helps.