You are definitely not lacking cabinet space. At this point, with the 30" refrigerator and 18" freezer, you have more than most homeowners. Do you have a second freezer elsewhere? 18" is just not very wide... and if you are used to storing large platters (of fruit etc) in a refrigerator, might want to consider bumping that up to a 36" wide.

a 12" wide pantry cabinet is nice for storage- if for food, it would be great if it had pull outs. Otherwise, things are going to get lost in the back. If for brooms/etc. fine as is.

I would evaluate your food storage needs - think about hosting parties and needing the refrigerator and or freezer width for items. Then see if you need that 12" pantry cabinet.
Hope this helps.

i do have a second freezer.

My thought is 12" is quite small for a pantry in a kitchen that size.

I would recommend going with a 30" freezer to match your 30" refrigerator. Woodman Design is correct about an 18" freezer not being wide enough for food storage. Thermador does a 30" as well. The design lines will be cleaner and the storage more adequate.

The 12" pantry may be too small as stated above and when adding pull out trays you have to allow for losing some of that space.

Good luck with your project!

I have a 12" pull out pantry on the side of my refrigerator (as well as a walk in pantry). It's perfect for lots of spices, oils, etc. It sort of depends on your lifestyle. Would you be better served with a huge refrigerator? I find no matter how much space you have, it will be used up!