Yes, moving while IN your seat, remaining hydrated WATER, and stretching are all good. Sadly,most flights I’m on are 5-10+ hours, so I’m sure that increases my risk. 
I think you are getting a lot of erroneous advice here. I recommend a business class ticket at the least, frequent chardonnay curls for exercise, and frquent trips to the restroom for keeping the blood flowing. So the aisle seat was good advice after all.
I do greatly appreciate at least economy plus seats. It makes life much more comfortable!
Write the alphabet with your toes every hour? The toe alphabet is what I do every morning, so I don’t limp along like an old lady when I get up.
That’s funny, the toe alphabet! As long as you do it fully, using your whole foot and not just your toes, that could be perfect!
Yes, flexing from the ankle.