Plans or pictures would help people visualize. But in general, I like the cabinet doors on the same wall to be the same widths. Take the filler into account for the blind corner cabinet.

Sorry, I couldn't get my images from my laptop initially. I've uploaded some of the different possibilities.

Do you mean all the cabinets along the window/sink wall (both to the R and L of the window) should be the same width? I was trying to find a way to do 18" width walls across but I'm afraid that would require too much filler on the blind corner cabinet and it will look awkward. Thanks!

You need the same negative space reveal around the window, with the same size cabinets flanking it. Start from there and use the subtractive method to see what else fits where

Which side is the peninsula?

It’s on the left side (when facing the window)

Ok. I like any of your drawings EXCEPT the second (because of the various sizes), given that the distance from the window in the peninsula side can match the other side.

Could we see the Kitchen as a whole? I'm wondering if it would be better to have the

(1) right cabinet either "die into" the right wall OR

(2) void out the corner and just have cabinets on either side (blind corners are the worst use of space, voiding often provides more usable space and is a much better use of the space overall) OR

(3) use an easy reach that might give you better door sizes

I'd have to see the overall upper cabinet layout in your Kitchen.

With our smallish kitchen, there are only two walls of upper cabinets - the set of 30" flanking the range/hood, and the ones for the far window/sink wall. There is about 14" between the second 30" cabinet and the adjacent sink wall. There will be a 12" depth set of upper and lower cabinets to the immediate right of the current POV, comprised of 3 x 15" cabinets across. The peninsula will have a 36" countertop, and an EIK is to the left of the peninsula (about 10' x 10'). There is a partial wall above the peninsula which is what comprises the 40" wall space to the L of the sink.

I am not opposed to voiding out the corner! Sure, I could use each inch of cabinet space but I also don't want to spend the next 20+ years staring at a cabinet design I don't love. And I love symmetry (more than I thought I would, apparently). We are looking at a slim shaker-style door.

I also considered using a blind corner cabinet that would give me an 18" door (so 18" doors across that wall), but then I'm concerned there will too much filler (about 4") between the door and the adjacent cabinet.

I guess another option would be making our wall cabs 36" high, and then doing 12" doors across - for some reason 12"x36" doors are more visually appealing to me than 12"x42" doors. This would be made of two 24" cabs directly flanking the window, and one 12" cab (probably for tupperware). I'm not very tall so the top shelf of a 42" tall cab would be pretty impractical anyway.

We have 99.5" tall ceilings and want a 20" backsplash height. That would leave me with a 7" space on top for a crown...which is doable? I don't want an ornate crown but would figure out some sort of flat trim for the majority of it.

Are 12" doors a terrible idea? Help!

Is 39” an option in your cabinet line?
I have 36” cabinets with 12” doors and they look fine.
Why the 20” backsplash?

Unfortunately 39" high cabs are not an option in my cabinet line (I asked specifically - figured it would be the perfect compromise!).

Will keep 12"x36" doors on the table! I'm trying to look at more kitchen photos with 12" wide upper cabs to get a better feel.

With our ceiling height I figure I'll either have a higher backsplash (20 vs. 18") or more crown molding height, and I'd rather have more room above my countertop appliances. I would rather not have any space between the crown and the ceiling (that will never be cleaned). Also hoping for anything that gives our kitchen a "larger" feel.