Here are the interior dimensions (W x D x H) for my H4082BM: 18" x 15.5" x 8.25" Because the upper broiling element intrudes into that height space, the highest usable vertical height is 7.5" (from oven bottom) or ~7" (on the glass tray), or less. Certainly no problem for a 9" x 13" casserole dish.

First of, congratulations on your good deals for these three units. They will serve you well. For ventilation and wiring purpose, you will need a gap at the back of the shelf behind unit. For combi steam oven, this is where the oven sucks in the air in. It will vent warm air to the front underneath fascia. So following diagram #1 looks fine. For the sentence "The cabinet housing must not have a back panel fitted behind the installation niche", this must be from a newer manual of the combi steam oven. For example, see newer 6805 manual vs older 6805 manual. In a version that I have it uses "Make sure there is no back wall behind the building-in recess" which means that there should not be a cabinet back wall right at the cut out area. See picture for air intake in combi steam manual in installation section. In terms of installation each is 18" tall, just need to be arranged such that coffee machine is not too tall, and speed oven not too low. Perhaps somewhere where the bottom of the combi steam oven is a little bit below bench top level. A combi venting warm air at the front is not an issue for comfort. I have only combi steam oven in my kitchen and its bottom is at the bench top level which is very convenience, but that would put coffee machine a little too high up, if it is going to be on top. Here is an image from mile-vs-wolf-steam-oven thread. Found a funny image on the web of Miele ovens, noted the coffee machine location.

Since you don’t use an oven frequently, it seems silly to spend the extra amount for the Miele oven. It’s bad enough to have to spend $2,000. I assume you want a 24” oven because of space constraints. You are probably also aware that there aren’t as many choices for 24” oven and even though they are smaller, they are more expensive than a 30” oven. When my daughter needed to replace an old 24” double oven she found only 5 double ovens in stainless steel and they were all too tall for her space. She didn’t want to do a kitchen remodel to get 30” ovens. She could not increase the height of the coutout in her oven cabinet without getting new cabinet doors. She opted to use a 24” single wall oven and a single speed oven/microwave. Bosch and Miele were the only brands that had the specs she needed. She choose Bosch’s model HBE 5451UC. It retailed for about $1,7000 but there were some rebates available at the time that reduced the price. AJ Madison still has that model on their website for $1,700. My daughter likes her wall oven very much. It heats up quickly and cooks/bakes evenly. She has had it for almost 2 years and has had no issues with it. Here’s a shot of her oven

Patricia - Thank you. "Features" is a highly subjective term and maybe no place moreso than in high end kitchen appliances. I could not care less about a single "program" in any device I've ever encountered in my kitchen. In fact, I think "programs" are generally a negative because they complicate the user interface and make it more difficult to understand what is happening (or has happened) to my food. My range will have them, too, but I'm not going to forego a range because I couldn't care less about "programs". My attraction to the speed oven is (1) size and therefore, presumably, faster preheat (I value my time and like to eat when I want to eat, so that reduced time is somewhat quantifiable "feature" to me) and (2) the double duty as a second conventional (albeit small) oven AND a microwave, giving me two functions in the same space - yielding a marked aesthetic improvement to the kitchen. If the thing was just an empty space that I could heat using either a conventional element with a simple dial to set the temperature, a microwave with just power settings and a timer, and/or both when I wanted, I'd be happy. What I'm trying to determine is whether I'm giving up any of those things by going with the low end Miele. It blows me away that the only difference to justify a $1,600 (41%) price difference would be some "programs". So I'm wondering if I'm giving up an actual heating element (or power in same) or the ability to simply control the oven. Miele, as seems to be par for the course in all high end kitchen appliances, makes it very difficult to get to the facts and just want to bullshit me with some special function that will simultaneously cook a baked potato, a steak, and a souffle, at altitude!