Can I just lay slate tile over a concrete patio without any bond material butting edges and them water treating the suface

You could do this but I would not recommend it. There will be a trip hazard and the tiles will wobble and shift, not a good walking surface and certainly not safe.

Not a good idea. Slate is a very durable but delicate material. You need to have a good base for the slate to rest in otherwise when stepped on wrong, it will definitely crack. And water will get under the slate as well causing problems with the slate cracking. Slate is best used on a dirt surface underneath.