They should be on different switches. As you said, the lights for the upper cabinets are decorative. But the undercabinet lighting is task lighting, to use while you are doing cooking and prepping tasks on the counter. To be honest, I had upper cabinet lights in my previous kitchen in the glass cabinets, and ended up rarely using them. So I didn't get them with this kitchen. But the undercabinet lighting is used all the time.

While you are at it, make sure the undercabinet lights are installed toward the front of the upper cabinets, not the rear. That way, they are lighting the center of your counters, not the backsplash. In addition, if they are mounted toward the rear, you will be able see the light strips when you are seated nearby. If they are installed toward the front, they'll be hidden by the light rail. Electricians don't like to install toward the front cause it is easier for them to install toward the back. Insist.

Install the undercabinet lighting switch in the backsplash. That way, it's an easy reach when you are working at the counter.

It depends about how you use them.

I dont like tons of switches or separate switches here and there so in one bathroom they are all ganged together and put in a specific order of use from closest to the door to farthest.

But in another bathroom I put one switch near the door and ganged the rest in an unobtrusive location and had labels made for them (guest bath).

In my previous kitchen I put the switch for some lighting inside one of the cabinets.

I personally don't like light switches in the middle of the backsplash for design reasons, but I agree you will want certain watches within easy reach.

Upper cabinet lights- you mean inside the cabinet lights? Whatever I suggest I have no clue if there is a code met or broken.

I would want them separate. No I have not had them inside my kitchen cabs but did have them in living cabs. I like undercounter for working but if I had lights for inside the uppers ... I would want them on own switch. Sometimes you want to draw the eye to your pretty things and nothing else!

In my mind if I want to get rid of the look of a switch I would put it IN a cabinet without glass doors of course so maybe a pantry.

I don't think there's a straight yay or nay answer to this. Think through how you use your kitchen, all the kitchen scenarios your family goes through, and what lighting will suit you best in those situations. Then make sure your switches will allow for those situations and call it good.

I grew up with a kitchen where the undercabinet lights were on a separate switch from all the ceiling cans. The cans are on all the time whenever anything is being done in the kitchen. The undercabinet lights are sometimes turned on as well during serious cooking projects, but that is pretty infrequent. They're actually used most often after all serious kitchen activity has ended for the evening (after dinner is done and all cleaned up), at which point only the undercabinet lighting is left on and then functions almost like a night light. The kitchen is pretty central in my parents' home, and we'd often have to walk through it in the evening or do something small in it like get some water. For those activities, the low light of the undercabinets was enough. Sort of like the lighting on an airplane when they turn everything down so people can go to sleep easily but also can still see enough to walk down the aisles safely.

When I was designing my own kitchen in an open layout condo, I went overboard giving myself options for lighting. It was/is my first experience living in an open layout, and I wasn't sure of all living/lighting scenarios we were going to encounter. We have three light switches for the kitchen. We have only one short stretch of normal uppers, so one light switch controls the lights inside (all the uppers are glass) and under those cabinets. Another light switch controls two cans that are above the kitchen sink and the counter right next to it. The third switch controls the other five ish cans in the kitchen.

On the one hand, it's a little annoying to have three switches. It's been years, and I still don't have the line-up memorized. I just randomly hit one after another till I get what I want.

On the other hand, I'm really glad to have the options. As it turns out, we almost never use the undercabinet/inner cabinet lighting. They're above a 30-inch deep counter, and so very little of the counter there is in shadow. Plus, compared to the ceiling cans, the inner/under cabinet light isn't super bright and is a cooler color that I don't find to be as friendly as I want my kitchen to be. It's more like cool bachelor pad party lighting and something that is good for resale, but it doesn't provide anything the cans don't do better during daily use.

When I cook, I turn on all the cans everywhere by hitting the other two switches. It makes the kitchen WONDERFULLY bright for serious-all-over-the-kitchen cooking, but that amount of light is definitely overkill for small kitchen activities. When I'm doing something small while my husband is watching something on TV, I turn on just the two cans over the sink (like a spotlight on that part of the kitchen) so I can see what I need to see while limiting how much light gets reflected in the TV screen. For all other kitchen scenarios, I just tap the easiest switch closest to the door which turns on five ish cans at once, which is plenty of lighting to do anything except serious cooking.

I don't think we have ever used the dimming capabilities of any of these lights.

I'm positive your mileage will vary, but I hope that explanation will help you to think of and to run through your family's likely scenarios.