Where I live the Miele installers do a pre-install site visit to your home and give you a list of things that need to be done before they will schedule the actual install. Pay attention to that as they might refuse to complete the install if those items aren't done to the installers satisfaction. For example they may ask you to put in a furring strip if they determine the opening is too wide (that happened to me).

Read the install manual carefully and measure. Then I'd call the Miele Concierge and discuss the installation requirements before you buy. I found the Concierge staff to be very helpful. If you tell them you'd like to reuse the door they will help walk you through that to help reduce the chance of problems at the time of install.

I doubt very much that the old panel will fit the new DW. Miele's are slightly narrower.

Agree with Stan Z's comments, if you have Miele's Concierge group do the install they will do a pre-install visit to measure things, cabinet clearances, power receptacles, water and drain access, etc.

I personally have had mixed results with the Concierge installers, however they are supposed to be a cut above any appliance dealer's installers. That point seems to trump any negatives involved.

I'll expand on the 'read the install manual carefully' comment, to point out there are multiple documents with install checklists and cut outs (cabinet dimensions) on Miele's US website for their dishwashers. In looking at mieleusa.com, I see that is still the case, there is the 'operating instructions' manual, which will have an install section, and there is an 'assembly plan' document.' If you go to the specification library (start at Architects & Designers), you will find a spec sheet, which may be a third document with dimensions.

In my experience there may be a fine point in one manual that is not clearly pointed out in another manual (this is not only for DWs), for example placement limits or clearances on an electrical receptacle (is recessed wall clock needed?), a drain hose length, or back of the appliance clearances to a rear cabinet wall. If you will have a plumber or electrician do some or the rough in work, give them copies of the relevant sections in the manuals, these guys work from specifications and drawings.

Wow, thanks so much for the extremely helpful responses!

About re-using my current custom panel - could they do the install without a custom panel at all? (in case there's a huge delay in getting a new one one made?)

The install can be done without a custom panel. I had my install done without a custom panel at first.

Good luck!