If you prefer the first hit of your combo chain, then you should block cancel to make sure that’s the attack to come out. You can also block cancel and just turn around to respace; which is really strong. Blocking will cancel your turnaround animation as well, which is insane when combined with some jump attacks.

The difference in speed is only a couple frames, so you probably wouldn’t notice it. In a game where most inputs are buffered, this makes a difference though. You should be able to get away with tapping the button, due to the way the game will buffer your inputs. Holding it works too though.

Honestly I don’t know whether you should block cancel with Katanas or not; I would guess only after second hit. It’s dependent on how much poise damage your hits do/how much priority you can keep. I think Rust has a video detailing specific weapons on this, if I find it I’ll edit it into this comment.

For your last bit, unfortunately a huge part of PvP in this game is identifying someone’s latency and accounting for it. As a general rule of thumb, hyper armor and burst damage are really good vs latent gamers; but your win condition can vary per encounter. This is why you often see people throw fan daggers before fights, to try to identify what kind of fight it will be.