I would wait on the whole replacement. Yes, appliances do vary, mainly the refrigerators. There is a standard height for cabinets above a refrigerator at 72", but some refrigerators are shorter, and many are higher, especially when you get into the built-in look. Stoves are fairly standard, but your current cabinetry may be limiting you to what size stove you'd need for a replacement if you wanted to consider a larger stove for your renovation. Microwaves and dishwashers are stand-alone products, so you can be comfortable doing those "piecemeal," as you said. The one thing you can keep in mind is that some renovators choose to get panel-ready dishwashers to blend in to surrounding cabinetry better. If that's the look you want, then replacing the dishwasher prior to your renovation could be tricky because you wouldn't have your final cabinetry material yet to apply for the front panel. Those units are basically unusable without a front panel because they are designed for you to install your own handle on top of the panel.

Thank you to both of your for your insight! It is really helpful and I really appreciate it!

We have a refrigerator from the late 1990s still running beautifully over 20 years later and will not be replacing it in our current kitchen remodel. My parents had a refrigerator they kept up through about 2013 that had been running, and was still running, for 50 years. Only the seal was bad, and it would have cost them a fair penny to replace the seal, so they bought a new fridge, but looking back I think maybe we should have just replaced the seal.

I understand. My microwave is at the point where I have to heat things for twice as long in order to get it hot. My frig is somewhat inconsistent on keeping things cold. The D/W could probably eak out another couple of years and the oven is usable (although would like to get a self-cleaning oven). So I think a Microwave replacement is in the near future at the very least. I take it your suggestion would be to go ahead and replace it and then worry about how it fits into the eventual rennovation down the road rather than replace multiple appliances at once?

Update: Just checked the labels. The microwave is from 2004 and I have to believe the other appliances (since they are all Amana and have the same front) may be of the same vintage. So we are at about 16 years of age instead of 12.

If your fridge is inconsistent, go ahead and replace it. You'll save a lot on energy costs if your current fridge is inefficient and you replace it with an Energy Star model which is a rating applied to any brand that meets certain criteria. New appliances usually last about 10 years.