I went from a freestanding to a slide in before I replaced my countertops. With the old counters I bought the rear filler strip which covered the ~2" gap at the back. New counters were templated so I could eliminate that filler strip.The rear filler for my stove was made for a 25" deep counter which worked perfectly with the original formica tops. If you have 25.5" deep counters (or something that puts the front edge more than 23 1/8" from the rear of the opening) then you might have to do something different with the filler. I'll have to check but I do think the manual listed a second option for those situations. The slide in ranges don't have sides. For my GE profile I could purchase sides extra if needed - in the case of it sitting at the end of a cabinet or if it were to stick out from the cabinet face more than 1.5" so you didn't see the bare frame. Nothing special needed to be done for the cabinets or countertops other than the countertops need to be level as you will lower the cook top onto them so it just touches since it overhangs the counter. If the counter tops aren't level you will either have a gap on one side or your eggs will roll to one side of the pan. My GE could fit an opening as small as 29 15/16" and ideal was 30 1/16." My exisiting cabs were 30 3/16 and I had new counters templated to match. You can't see any gaps since everything is covered with the cook top. The front edge of the stove sits pretty tight to the cabinets as well as the trim strips on the front edges are flexible for lack of a better term. I can post a photo of my range if you like.

If you go to the bottom and do a search on "unfitted", you will find a number of discussions, with links to Web sites, books and magazines where you're likely to find pictures of the kinds of things you might take inspiration from. Many of them are European, where the approach is more common. It tends to make Americans anxious for some reason. That may answer some of your initial questions. Enjoy!

Buffalotina here... When I remodelled my kitchen I already had a white fridge (Amana, nothing fancy) and a white Miele DW which I absolutely love and both were fine and not ready for replacement. The fridge is tucked away out of sight in the breakfast nook and looks OK there because there are no cabinets and the other stuff in there is utility white wire shelving, racks etc. As you see I did the Blue range. I agonized over whether the white DW would be OK but I decided to go ahead with it rather than trying to panel it or anything. My rationale was that as you look at that wall the backsplash is white and the white DW is also in the vertical plane and so I think it looks fine. I also have the small freestanding white cabinet that stands in the vertical plane. Also my cabinets are a very yellowy cream (Brookhaven French Vanilla) and so there was no problem with white on white where the whites might not look good together. That all said if and when I replace the DW and fridge I am tempted to go stainless... but it will probably all depend on what fridges are available at that point. Right now I am lusting over a Liebherr....and that is only in stainless... and when push comes to shove I may not be able to bring myself to spend that much on a fridge. I think I would be inclined to go with what looks more period for the 1915 house...and perhaps showcase the white vintage range and keep it the only white appliance? Good luck!!!

Your decision of slide-in vs free-standing will impact the counter installation. Counter material will not impact selection of range style. I switched from a free-standing to a slide-in range a few years ago and the range came with a little strip to fill in the gap behind the range. If I'd installed new counters, I would have had the counter fill in that space instead. The way that my slide-in installs, it may also have been beneficial (though not required) to notch the counters slightly in order to snug the range closer to the back wall. So when you've selected your range, make certain you have all installation instructions available prior to installation of the counters. A 30" range should be just that: 30" wide. You can usually check out installation instructions and specifications online to make certain, but as long as you currently have a 30" range in the space, the wide should be perfect for any other 30" range. Personally, I like the look of no built in backsplash on the range. That was my primary reason to switching to a slide-in. However, I've since found several ranges that are free-standing and have no built in backsplash. So, make certain you look at all of your range options before you make your decision on slide-in vs free-standing.