Actually, it's the stove that could use a dedicated hood for venting. Microwaves usually vent into the room, as do all wall ovens. They used to make wall ovens that vented outside, but they had to design some for people who couldn't do that and so they added filters and stuff on the high end, and stopped worrying about it altogether as people stopped cooking as much. I once had an over the range microwave in an apartment. While it theoretically vented the range, I'm pretty sure the microwave itself vented into the room. It was a long time ago...

In terms of looks, you have many options. Three high stacks are rarely comfortable, so I wouldn't suggest two microwaves and an oven together unless you want the oven at floor level like in a range. You could, instead, do an oven on its own or stacked with a warming drawer or something and a separate stack of your two microwaves. And for that you could chose between fancy built in microwaves and less fancy freestanding ones in cubbies, perhaps with trim kits for a more built-in look. Or you could stack one microwave with oven to match, and do a contrasting microwave (or matching) at a different point. If different people are doing the microwaving, that would work. For instance, a lot of people like to have the microwave next to the fridge for zapping a snack or sandwich, but for your dinner habits, one with the oven also makes sense, so you could have one of each.

BUT, let's talk cooking and budget. Do you have some money you could spend? Because heating all those leftovers would be a lot easier, and better, if you had a combi-steam oven. That's a convection oven (some also have broilers, now) which also has steam settings (you fill a tank, or have it plumbed like a sink). They're expensive, though (thousands of dollars), and you would probably still want a microwave for a quick zap here or there. What you can do in a combi-steam, however, is heat different kinds of things, and better yet, composed plates, without them getting weird or over cooking. In theory, you could even do this in a regular oven with a pan of water for the steam, but that takes effort. The results and timing would be a lot better than all those microwavings. For looks, you could stack a microwave over one oven and a combi-steam over the other, and have no symmetry, or stack the microwave and combi-steam together, or do all three apart, if you have the room.

Additionally, since in a new kitchen you're likely to develop new cooking habits, again, if you have some money to spend, you might be interested in a speed oven. Not as expensive as a combi-steam, but more expensive than a built-in microwave. A speed oven will work as a convection (hot air) oven (and some even have a broiler), as a microwave, and as a combination of the two. You can cook things much quicker on the speed settings because the microwaves get the interior heating up while the oven part is doing all the cooking transformations from the outside in. If your regular multimicrowaving style of getting dinner out is to save time, perhaps during the work week with a cooking day on the weekend, you might find that there are a lot of good dinners you can make fresh just as fast (maybe just do some advance prep), and nicer from not being rewarmed. You can easily stack that over your oven and put a microwave only elsewhere.

I have one regular oven stacked with a combi-steam, and a speed oven on the opposite side of the kitchen. I don't microwave meals, but I do use the microwave settings of the speed oven for melting the cheese on a sandwich or reheating a cup of soup or pasta. Those all could be done better in the combi-steam, but have enough of their own moisture that they don't need it for that, and for two minutes of zap it's not worth the wait. Everything else gets heated in the combi-steam.