I'm running Silver Flute 6.5's in small ported enclosures under my seats (page 2 of build log here to see them)
https://www.caraudiojunkies.com/show...le-Build/page2
I was curious to try this because I was getting major 120hz cancellations in my doors, and the outside plastic door handles would buzz no matter what I tried. I was also intrigued by how well the 'Flutes modelled (~0.15 cu.ft, tuned to 70hz, 2" port). Low group delay, very efficient and crossed at 75hz they theoretically won't hit xmax until 200-ish watts.
Here's my subjective answers to your questions:
1: I wouldn't plan to cross them over much higher than 180hz or so (I'm currently at 170, 24db LR). Higher than that, for me it starts to negatively affect the soundstage and gets a little muddy. You will want a midrange that can handle crossing that low.
Bottom crossover will depend more on which specific drivers you're running, their enclosure size and your preferences. I'm crossed at 74hz 24db LR.
2: In my case, I have much better midbass impact than I did in the doors, with fewer cancellations. The high-tuned ported 'Flutes have a bit of a PA-style sound to them, very snappy. I think because they're so efficient and I'm not playing them that low, you don't really "feel" them under you like you'd expect. They don't stage quite as nicely as my door midbasses did, the bass isn't as far in front of you. They blend with the sub surprisingly well. They do have a peak around 112hz that I have to tame with EQ (my doors also had a peak in this range, but it wasn't nearly as strong).
3: I'm a little confused by this question. I wouldn't run the Anarchy's under the seats and the WD800NEOs in the doors at the same time if that's what your asking. I'm guessing the Anarchies will work in a small enclosure, but they're very deep so they may not fit under your seats. I don't know what the WD800NEO's want for an enclosure. Some folks have cut holes in the floor of the car to make infinite baffle enclosures for their underseat midbasses.
I should mention, I'm not a mega-sq guy. I like fun, punchy, dynamic and non-fatiguing sound in a moving car, with a nod towards sq.