Depends on the door for access, and the organizational needs. Sliding doors or barn doors? Bifolds? Double swing? Shelves are not going to span 8’ or even 4’ without some type of intermediate support. Brackets? Vertical dividers? And why 18”? That is fine for lowers, with pull outs, so you can get to stuff in the back. It’s too deep for uppers, and canned goods in the back will be unknown and not rotated. Will there be a counter srction? Counters are best when unbroken. Etc.

The details matter.

show a general sketch how it fits in to the layout. why no counter in an 8 foot stretch.....? five feet of pantry and 3 feet of counter with uppers and lowers sounds about right ,,,,but it depends.....

I think you could get prettier doors on 2 @ 4', but I'd like to see a sketch of the room.

I'd prefer one 8 footer because I'd have a hell of a time remembering which of the two pantries an item I am looking for is stored in and I'd drive myself nuts going back and forth. However, it all depends on what kinds of doors you want to use. What were you planning on for the 8 footer?

How perfectly odd to not know where things in your kitchen are. Like, if you’re looking for a teaspoon, do you have to go through three cabinets before finding one? Are your coffee mugs tucked in with the pasta one day and the next they are near the dish soap? I could, with perfect accuracy, tell you which cabinet you’d find the coffee in, or the cereal, or the crushed tomatoes. I might not be able to tell you how many tins of smoked oysters I have on hand, but it certainly wouldn’t be a maddening search to find out.

I prefer pull outs, so easy to see and use.

What would the doors be like? I’d love an 8’ pantry, my mom’s I think was 6’ with bifold doors. At first I though maybe 8’ but the panels on the doors were not 2’. She had another closet with 2’ panels and man, was that heavy.

Using pocket or French doors.
Want to see everything at once, without opening multiple doors and/or pulling out drawers.

Basically what you are saying is the doors will never be closed, so you might as not do them. Just do built in pull out cabinetry, and a section with a small counter.