You're right. When you spin faster you can't help but end up with more weight on the saddle. Like most things in life you want to try to hit a happy compromise. I'm not really sure how much % of my weight is on the saddle when I'm riding but obviously it goes down on the hills and increases to "mostly" when I'm just cruising along with little pedal resistance. I know that on the flats I tend to pedal in bursts and then coast while standing on a pedal to ease the pressure on the saddle. Then pedal some more, coast, pedal, coast..... It works for me and I really find it's tough on the backside when riding with a little group where it's important to maintain the pace because we're all drafting off each other. So I tend not to ride with these drafting groups anymore. But that's just me of course.

You've got to watch that errant hand pressure stuff. You've seen now sensitive the bars are to pressure. So yeah, a twitch at the wrong time can lead to a side trip through a flower garden if you're not watching for it...

Not sure what you mean by "knees tight". If you ride with too much internal isometric stress in your legs you'll tire sooner. Try to relax and if you think about it at all think about easing up on any residual pressure that tries to limit your feet and knees from moving in a circular way. Relax what isn't needed for the work and apply what is needed.