I've been reading and studying people's thoughts on kitchen layout, and have come up with my best attempt at modifying our current kitchen to be more family-friendly without breaking the bank.

Our current kitchen layout has a peninsula which divides the room and leaves space for a breakfast nook by the 49" window which we don't need. I want to make use of the whole space as a kitchen and add an island. We will be re-using as many cabinets as possible while re-configuring. (Any item with a checkmark means we have it already.) Sink and oven can't move. We are not modifying windows or doorways.

Under the left window we thought a window seat would be lovely, but are stuck with how to best manage the top left blind corner. Any ideas? I would also appreciate any other feedback on the kitchen layout I've come up with.

Our kitchen is 18'6" x 14'6". Cabinet to cabinet from sink and oven walls to island is 42". (6 inches per square.) Do the aisle widths work?

New to this, but trying to learn. Any feedback would be appreciated!

You will have a lot of kitchen space, but since prep almost always happens between the sink and range, it looks like you will be prepping on that 36" end of the island. To me, that's a shame.

Would you answer some Qs:
Where do all the doorways go?
Can the Utility Closet move?
Is the top window too low to put cabinetry underneath it?
If the top window IS too low, is that window 23.5" from the wall to the window, or the wall to the window TRIM?
Do you REALLY want a window seat? I think it's cute, but it kills the storage there and I can't imagine sitting like that in the corner when the island is right there - I'd feel like I was in time-out.
Is your family really short? If not, 12" of overhang on the island is really not enough kneespace; 15" is the recommended minimum.
Do you really want a desk?
If you really want a desk, are you sure you're OK with having it next to the Fridge?
Are you willing to buy ANY cabinetry; if so, how will you integrate it into the kitchen? Paint/stain to match existing, or have it be a different finish?

Without knowing more, my general thoughts are:
Put Fridge on left wall. You will now be prepping on the long side of the island.
If window allows, also put Desk, mini-fridge, or existing cabinet on left wall - take your pick. If window does not allow, run window seat all the way into the corner.
Increase top aisle from 42" to 48" to allow for the increased traffic flow now that the Fridge is moved
Increase your island overhang to 15" deep
Buy new shallow (12" deep), tall cabinetry for the bottom wall - the whole thing becomes pantry space. You can try to have them match the existing cabinets or have them be different. Actually, the deep Pantry in the corner can stay because it doesn't intrude on the aisle between the island and bottom wall.
This will give you 48" aisle on the top and bottom. You will have to play around with the Fridge aisle.