Dual Wielding with multiattacks is elaborated upon in the errata. No clue where to get it, sorry. In short, it states that if you're dual wielding and use lightning attack you get 3 attacks with 1 weapon and 1 attack with the other weapon. The same applies with swift attack, except 2 and 1 attack(s).
You can also use lightning attack with a pistol in the "off-hand' (I'd hope you're ambidextrous at this point) and get 3 attacks with the melee and 1 with the pistol. In this case you'd need Dual Wielding (Ballistic) AND (Melee).
No idea. Melee weapons are pretty restricted in their upgrades in general. I think there's Lathe and Mono (but mono only works for primitive weapons). Also, by Force do you mean Power Sword?
I'd vote yes, but you can only operate so many weapon in one round. Certainly be nice to have the versatility if you happen to be made of money. Note, I don't think flamers can be mounted on wrists, but that might be Macharian's work, not official stuff.
Okay, for opposed checks:
Both parties roll. Often, one party is considered an "aggressor" of sorts. For example, disarm is an opposed WS check, with the disarmer being the aggressor. If both parties fail their checks, the aggressor's action fails. If the aggressor fails his check and the defender succeeds his check, well, then clearly the aggressor's action fails. Now for the tricky bit: If both parties succeed, and the aggressor succeeds by more degrees of success than the defender, then the aggressor's action succeeds.
e.g. Strin is trying to disarm a cultist. They both have swords. Strin's WS: 40 and the cultist's WS: 50.
(Strin's roll (Success(degrees)/Fail)) (Cultist's roll (Success(degrees)/Fail)) (The outcome)
(30 S1) (30 S2) (The disarm fails.)
(62 F) (75 F) (The disarm fails.)
(15 S2) (30 S1) (The disarm succeeds.)
(38 S0) (52 F) (The disarm succeeds.)
(8 S3) (42 S0) (The disarm succeeds and Strin recovers his opponent's weapon (assuming he has a free hand))
Man, I don't even know what biomantics are.