A lot of questions...
First, yes- trim after sizing. Sizing stretches the brass...which is why you need to trim in the first place. Of course, only trim when you're at max length, some go longer by using a Sinclair chamber gauge to verify their leade can accomodate longer brass without crimping the bullet.
Cleaning primer pockets, to each their own, I do not.
I have test results from a shooter using an RSI pressure trace that prove "clean" primer pockets have no effect- in fact, they result in higher deviations. I'll post a thread on this test when I have the time.
On a progressive- yes- remove the shell from the shellplate after sizing/decapping. I do them all at once, then just start from the primer station.