I 'bake' my egg shells for about an hour in low heat oven, then smash 'em up, I don't clean them either! I briefly looked at your links - I'm going to have to study them in detail, I so object to paying an 'arm & leg' for stuff you can make yourself. I'm pretty good at basic woodwork, however...
Yes to the grit. The oyster shell you can either feed separately or add to feed - your choice. Once they start laying you can crush up the egg shells and feed it back to them.
Sue