It's slightly hard to model without... Anyways.
What I'm thinking.
Tweeter crossed over at 8khz. 4rth order. It'll need some series resistance with it. How much I'm not sure, but I want to do like with the midtweet and try to push it towards current driven response a bit. 2ohm maybe?
Midrange/midtweet 3rd order on both ends. Crossed at 8khz and probably about 1.2khz (?). The reason for this is I'd want to vent to the outside with tiny holes that could be drilled to make it aperiodic, and I know the low end is going to trail off so it needs to be high enough to prevent that (I'd go lower if it could, to 1khz). It'll provide some extra damping. This is good because I want to put a fair bit of resistance in series with it. This will have to be tuned by ear most likely. But the intention is to move it into being more current driven, and let more of the physical properties steer it.
For a midbass I'd use the Zaph ZA14W08, 2x per speakers. I'd use them in bipole. Because I'd have them ported and running aperiodic in parallel (crazy I know, the port gain isn't terribly important). I'd expect it to run maybe into the 40hz range with a sensitivity around 87db (it'll need some BSC like crossover work because the gain from the room will be too much). The ape vent can be on the top, and the port out the back above the woofer. The box would have a little bit of an L shape in a way because the tweet/midtweet would be mounted on the front without being inside the box, to let the mid run aperiodic.
I could be totally wrong about the whole thing but... just an idea. I think it might be fun on a tube amp. It'd sound serious gusto, and hopefully pretty articulate without a bunch of feedback.
I would suggest using the same order crossover throughout the design to avoid phase issues. The midrange has very good dispersion to 5K. When I used a transformered ribbon tweeter I crossed it higher, but with a planar tweeter you have more flexibility to go lower. I also find the optimal sound quality under 7500. Over that, I'm not fond of how it sounds, personally - although a bunch of them in a room all over the ceiling for surround up to 22K do sound fun LOL
There are a lot of good woofers in the 5" - 7" range. I have found 6" to be the biggest while keeping the MMS low. Keep in mind that this mid can match to a pair of 10" drivers in a pro-monitor application. That said, the "aural weight" can be a concern. Dual 5's will sound really great - but if you do want to move air, it's pretty common to cross to a good woofer, not sub, in the area of about 120 - but that's a personal choice. My Ruby's are a 2-way planar with a 5" and they kick butt. People wonder if there's a sub in the room.
Aluminum and magnesium or other exotic woofers are great. What you want to make sure is you don't cross too high so you don't introduce ringing from the cone. A great example of a well-damped speaker is the SEAS Excel W15CH001. Really a good driver - but $$$.
There are also some great offerings from ETON if you want to take out a second mortgage. That said - you can carefully select a good-priced mid-woof if you do your homework. When it comes to caps in the crossover - well, argh... My speakers use about $500 in caps per speaker my OEM cost. I keep them in a safe
Sounds like you're having some fun. You combo would sound insanely good with a tube amp. With a good listening position it should compete with headphones. Given the value of the mid-tweets - be careful on your mid-woof selection. While price isn't everything - make sure it specs correctly. I have a closet full of woofers I thought would work and they were garbage. It's like cooking - a lot of tasting before you are willing to serve it at a dinner party