^ I have never actually measured, but I'd bet that it's about a meter diameter at full extension. You can lock the legs securely at less than full extension, but, of course, it won't be quite as stable.
Yes. You can make the legs very narrow, but it would be a bad idea. I use a heavy weight bag when the stand is set high.
If you want to mount full-size mics (not tiny lavs or something like that) and you need tall height, your options are:
A. Wide base (preferably with some counterweight)
B. Narrow base but HEAVY weight.
C. No base, but a rigid, semi-permanent attachment to floor or structure (heavy-duty clamp, bracket / bolt, etc.)
If you don't have one of these, you run the risk of damage to your mics and surrounding humans.