Is it possible to extend the kitchen so the west wall extends to the same ending point as the Refrigerator & small wall to the left? It would give you room for much needed storage. If you look at what I've posted below, you'll see that I put in a pantry cabinet across from the refrigerator w/a MW shelf to...

• Give you a lot more storage...you may even be able to fit 2 cabinets there. I don't know the exact dimensions of the pass through, etc., so I'm not sure how much room you have there.
• Bring the MW down to chest level and more easily accessed (no reaching across counters)
• Keep it on the perimeter for snackers but still easily accessed from the kitchen for cooking
• It's not in the way of the DW
• It's still near a water source
• It's directly across from the refrigerator & freezer where most food for the MW comes from
• I put a lazy susan in each corner b/c you can fit a lot in those things! I fit all my pots & pans in a 36" lazy susan in my old kitchen.
• 18" or 15" traxh pullout to the right of the sink...makes it accessible from main/cleanup sink & range

As to the prep sink...I think you should keep it b/c w/the size of your kitchen I think it will help to keep others out of the cooking, prepping, and cleanup zones.

Something to think about: 30" deep base cabinets & counters. Your kitchen is 10' (120") wide:

• Center of kitchen: Deeper cabinets/counters...31.25" + 31.25" = 62.5" so there is still a 57.5-inch aisle (4'9")
  
• South wall: 60" left & right counters + 36" range = 96", which gives you 12" on either side of the range, for the lazy susans;

  If you have a 48" range, you would have 6" on either side, but that wouldn't allow you to have the lazy susans since you need at least 9".

So, working from Bmorepanic's drawing...here are three suggestions...

The first one leaves your refrigerator as-is and puts the pantry on the DR wall.

The second switches the refrigerator & pantry cabinets b/c it would allow you to get a cabinet-depth refrigerator and recess it into the "new" wall.

The third one fills in that area b/w the small wall to the left of the upper kitchen all the way to the kitchen to give you a walk-in/step-in pantry...not sure which since I don't know the dimensions of that area. If it's at least 3', you could fit a walk-in w/door; if it's only 2', it will probably be only a step-in accessed from the LR (sorry about that...but at least it's closer than the mudroom!)

Layout #1...refrigerator on outside wall

Layout #2...refrigerator on DR wall

Layout #3...Walk-in Pantry (Note; If a step-in instead w/access from LR via bi-fold or other doors, then the shelves would go on the other long wall and you may be able to have short shelves on both short side walls)