1. Is there a preference for or against quoting part of someone's post and then referring to that in the body of one's own reply?

I certainly prefer it -- especially if there are intervening posts. Otherwise, it is hard to tell what it is to which you are responding.

2. Shouldn't one have something original and meaningful to say when starting a new post? ...

Ideally so, but if everyone followed that, we would have perhaps 10% as many top posts!

...(I'm reticent to top post very much because I feel I'm not qualified, but some posts do move me to reply - is this bad form?)

Not unless you post something really stupid or offensive (not that anything of that sort would ever happen here!)

3. What is the protocol when one finds oneself filled with loathing toward a poster...?

If I had a good answer to that I would be rich! Sometimes I find obscenity-laced responses make me feel better, but usually not. Pure trolls are usually best just ignored.

4. Pray tell PLEASE what is the best way to find good posts, and threads in which one has posted but somehow seem to disappear?

Seems to just take some time to learn which posters consistently put up good material that stimulates good discussing. Easier to learn which ones to avoid.