What about behind the electric stove? maybe then stainless or subway tile ?

I would stay with only the penny round backspash, not mix the two, and not the 4 inch all along the counter. Like this:

Sticking with one surface will look best. i personally would choose a larger size tile. your kitchen looks beautiful so far!

Well, I'm no pro so they may chime in..... using both materials for backsplash is kind of a big no no (having a 4-inch backsplash and then another backsplash to finish the wall). Given the condensed space you have, probably best to stick with one choice rather than making it look like you wanted everything you like squeezed into the space. With concern for behind the stove, perhaps that could be stainless steel, then everywhere else your favorite one of penny tile or beadboard. If it's penny tile you prefer, consider looking at some samples with a little more character to elevate the space.

Penny tile will always read as a bathroom floor misplaced. NO. no. no. It doesn't suit a kitchen, at all.

No matter what it is for splash? ONE material only for the entire 18" and behind the cook.

I dislike peeny tile anywhere that huge nimber of grout lines never my choice . I aslo do not think painted beadboard is an ideal backsplash . Choose a simple backspash that can run everywhere even behind the stove take it to the underside of the caninets if you like but all one materil no white grout and I lkke the matching grout with glass subway tile in small spaces .

I'd only use one material for the splash in a kitchen this size. I personally would not want to clean that much grout in a kitchen. But, if you like penny tile, go for it. Who cares what other people think? It is your kitchen.

I would take care to pick the right color grout, otherwise it can look too busy. And get a great installer so you don't end up seeing the lines between sheets, and can get good cuts on the bottom row.

This top pic is what NOT to do with penny tile - bad grout color, poor installation. The other pics though look great.

"And get a great installer so you don't end up seeing the lines between sheets" Yes to this! I'd go so far as to remove some of the rounds on each side (like every other one) so that sheets can nestle together. I wouldn't expect a tiler do that, but hopefully they'd be ok with the homeowner doing that to get the tile sheets to mesh.

There is tile that looks like beadboard if you wanted to do just a beadboard look, but most of the ones I've seen are fluted and dimensional enough that they might be difficult to use as a backsplash. Worth investigating maybe?

I disagree with Jan. Happen to love penny rounds and using them in backsplashes is a great option. But no, don't use both materials: