Listen. If you think you can do better, then DIY and good luck to you.
I would not design it myself, I would turn to meniscus for the design and advice needed.
My initial response to friend's suggestions that I can build a better speaker than those built by high end companies was "no way". But if I turn to someone with experience like meniscus than there is a chance.
At one point, with a budget similar to yours, I was planning to build a set of speakers based on Boehlender Graebner "ribbons", similar to Genesis and Wisdom designs. More like the Genesis with an array of ribbon tweeters since the Wisdom ribbon, which handles high frequencies better than the BG and earlier Carvers, is proprietary. However, a pair of Genesis 350's popped up for less than it would cost to build and probably far better than any feeble attempt of my own. If you weren't aware, Genesis is the company Arnie Nudell formed after selling Infinity but relatively few people have ever heard the bigger ones outside of CES and other shows.
The BG ribbons are available from Parts Express and the new DAB-1 active xover from Wisdom handles the necessary notch for resonance to extend them down past 100 Hz. From that point, an active sub or something more DIY would take over.
Yes, larger Maggies work best in larger rooms like most speakers with large sound radiating areas, which would include the big Infinitys as well, and also require careful placement for best results.
I think I read somewhere recently though that Magneplanar delivers smaller models, like MMGs, with ribbons as well these days and these might work better in a smaller room. This might be a very cost effective way to test the waters.
"How can I match or supercede high-end companies that have all this talent and measuring instruments that I don't."
That's the thing about the DCAB-1 (sorry, spelled it wrong before), it has real time analysis. Wouldn't tackle a job like this without RTA. I still flirt with the idea of using dual BG ribbons in series, partly to raise the impedance, but I'll probably never do it. I'm happy.