1) What did I buy?
IQ280, 645DF+, Alpa TC
2) Why did I buy?
I subjectively find MFD to be better for my studio portrait work and landscapes than my DSLR or mirrorless gear. I don't know how to quantify that subjective feeling. Color rendition? Tonality? More deliberative photographic process? Not entirely sure, but it feels right.
3) Do I like the stuff?
4) Is it better than D800E/Sony A7r or whatever?
I don't have a D800E, but do have an A7r. I've only shot portraiture with the A7r, and have limited experience from which to draw conclusions. I'm not itching to ditch my IQ280 based on early results from the A7r, certainly not in the same way that my Fujifilm X-Pro1 has almost completely subsumed the position that my DSLR held in my camera hierarchy for the work that I do.
I have not tried the A7r for landscape work given that I don't really have the optics for it to give it a fair shake against the IQ280 / Alpa / Rodenstock trifecta.
5) Is it better than my 5D3?
For portraiture yes. For landscapes yes. Mostly. (I still reach for the 5d3 when I want to do crazy HDR shots.) For action photography, good god no. For available light, candid photography, no. For that, I actually prefer my X-Pro1 to either DSLR or MFD.
6) Is DR better on IQ280 compared to Canon I have?
Don't know. Never thought to run an experiment to see. Probably won't bother since it doesn't matter for how I use my gear.
7) Is colour rendition better?
I think so.
Is aliasing an issue?
In theory yes. In practice, not so much.
9) Do I use the stuff?
I use my IQ280 daily.
10) If I do something important, will I use the MFD or resort to DSLR?
I use MFD for almost everything I shoot.
11) What is the main advantage I see?
Color rendition, can use the back on either a 645 body or technical camera, forces a more deliberative pace which I enjoy. Overall a bunch of factors come together to yield a subjective quality to images that I personally prefer to captures I get from my DSLR.
12) What are the main disadvantages I see?
Autofocus, poor noise performance as ISO increases, 645DF+ plus back and MF lens is heavy, expensive, there are features that I miss from DSLR-land (like flexible exposure bracketing) that I have very little hope of ever making their way into the very slowly developing 645DF+ "platform"
13) Are the pictures using MF better?
For studio portraits and my landscape work, definitely.
14) Are the MF pictures better "out of camera"?
15) Is the aspect ratio better?
Yes, but that seems like a very significant matter of taste.
16) Would I buy the MFD equipment again?
17) Do I regard it as a bad investment?
I don't really consider it an investment, so no.
18) Do I enjoy it?
19) Much of my photography involves travel by air. How do I handle it?
I never check my MFD gear, and never will.
20) I will go on a workshop, what equipment will I take?
I've never attended a workshop.
21) Can I see differences in printed images?
Yes. Even at A2.
22) Is MFD fun to use?
For me, yes. Very much so.