What, exactly, do the following settings do? I've looked through the CS Wiki, and they don't have any pages that describe them.

# fRumbleBlockStrength# fRumbleBlockTime# fRumbleHitBlockedStrength# fRumbleHitBlockedTime# fRumbleHitStrength# fRumbleHitTime# fRumblePainStrength# fRumblePainTime# fRumbleStruckStrength# fRumbleStruckTime

Pretty sure these settings are for the Xbox controller and determine the 'rumble strength' applied when your character gets hit.

And being Xbox settings, there would be no need to mod them in the CS since its PC only.

My next question is this: does modifying the following setting have any actual in-game effect on the duration & magnitude of potion and poison effects?

http://cs.elderscrolls.com/constwiki/index.php/FPotionMortPestleMult

Furthermore, when I try to create possible poisons through the http://www.uesp.net/oblivion/alchemy/alc_calc.php, I sometimes get formulas that have as many as five effects. If I edit the setting "http://cs.elderscrolls.com/constwiki/index.php/IWortcraftMaxEffectsMaster" to a value of five, would that mean that I would be able to see and use all of the available effects in the poisons that I create?

Yes. I use it in my http://www.tesnexus.com/downloads/file.php?id=32365 mod, so that the player makes less effective potions when in the wilderness, and it works.

I have never used this, so your guess is as good as mine.