I would not do both .

How much weight will likely be placed on these shelves? Whatever is used for support should be rated to exceed that load (after also taking into account the weight of the shelf). Floating shelves should be anchored to solid structure (i.e. framing or barring that solid blocking should be installed between the studs). The supports if hidden should be installed first then the wall paneling installed after.

None of the above. Both are the 10’s equivalent of shag carpeting of the ‘70’s.

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Don't fall trap to the shiplap trend. It's fading (finally), and it's rarely appropriate in homes despite what Joanna Gaines has people believe.

Like anything if it is done in moderation and its what YOU like go ahead. It does add texture and if used as an accent can set the "look" for the room.

Shelves especially in a kitchen require a lot of pre thought. Go take everything your going to put on one shelf and weigh it. Dishes and glasses are heavy.

You should use appropriate floating shelf brackets which are about $100 a pop or you can make your own. The shelves if floating should be a torsion box design which offer the most strength. They do require a thick shelf. Another option would be to use a good hardwood at least 8/8 thick (1 1/2" planed).

I would install brackets, ship lap and then shelfs.

By the way every decorating idea is a trend that will go in and out of style.