I have a small kitchen - it's a galley with an 8' run of counters but no uppers on a portion of the counter. However, since the wall of my dining area runs along the same wall as my kitchen, I effectively extended my kitchen storage by adding cabinets to that wall which are designed to look more like a classic hutch/buffet.
I opted for a Bosch side opening wall oven with a microwave drawer below. This provided me with the ergonomic benefits of a side opening wall oven as well as having the microwave off the counter and yet still ergonomically functional. I had almost NO counter space prior to my remodel - your island provides you with a lot of counter space.
It looks like your design plan includes a double bowl sink. I would ditch that and get a large single bowl sink with a ledge which effectively expands your counter space. In my small kitchen I got a 36" sink with a cutting board and drain board that fit in the ledge. Therefore my sink has become a very functional counter for prep - drying dishes if I hand wash. It's actually more functional than a regular counter would be because all the detritus of prepping and/or thawing is contained right above the sink so the counter never has to deal with dirt or chicken juice or whatever.
The pros of a wall oven are obvious since it is far more comfortable to use than below the counter oven. The cons are that you lose some storage and some counter versus a contained stove; the cost of the cooktop and wall oven are generally more than a comparable stove would be; the cabinets would be a bit more expensive since the stove replaces cabinets versus needing a cabinet to hold the cooktop and a tall cabinet for the wall oven is probably more expensive than a more standard lower and upper in that space. I don't know what my cost differential would be because my bid was for building the cabinetry to my exact specifications and I didn't get pricing for each cabinet.
Regarding storage, you will have storage below the cooktop - I have two drawers as well as in the tall cabinet housing the wall oven since I have drawers below and a combination of "tray" storage and another storage component above the wall oven.
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Island and built in
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