It says that techmarines start with a common cybernetics enhancement when made, but it doesn't talk about any other restrictions. Does this mean that a techmarine can take the servo-harness, even though it normally requires 50 req to take and a reknown of Famed just for the common quality servo-harness?

It states in the rules that a character is normally afforded one attack a turn, with the exception of two weapon wielding, swift attacks, lightning attacks, and etc. But given that Dark Heresy had a revamp of rules that became proactive for the Deathwatch rule set as well, allowing anyone to dual wield at a -30 cost, -20 with Ambidextrous, and a -10 if also having the appropriate TWW talent for the weapons being used, what does that mean for the servo-arm/servo-harness? Does a techmarine with a servo-arm get to attack with the arm as if it were independent? The techmarine still roles his WS for it, so it makes sense that it's not independent. So then does the techmarine consider it an off hand weapon? Is he ambidextrous with his servo-arm and not suffer a -20 penalty? Can he attack with his servo-arm and both hands in the same round? One attack per hand plus servo-arm? Can he dual wield in one round with his hands then use his reaction for the servo-arm, effectively attacking three times a round?

Does the servo-arm replace the servo-harness? Can he use the servo-harness to attack once per attachment on his harness? So could he attack with two servo-arms, flamer, plasma pistol, and once per hand in the same turn?

Techmarines, what do?

You must meet the renown requirements for any gear you take unless GM says otherwise.

Roger, roger.

Also, the Servo-Harness requires the Servo-Harness Integration Talent; available at Rank 4.

Page 177 Deathwatch Core rulebook

"The Servo-Harness Integration Talent is required in order to use a Servo-Harness."

You may not combine Attacks of in-hand weapons and servo-arms. Even if you have all the talents normally required for multiple attacks.

It is either servo-arm/harness attacks or in-hand attacks, unless you spend your Reaction to make a SINGLE additional Standard Attack.

See the other post you made for additional clarifications.

Yes, the harness replaces the normal servo-arm.

Even when using the servo-harness, you may not make more than one normal action that has the Attack subtype a turn. You may also not normally do the same action more than once a turn. In order to attack with more than one arm with the servo-harness, you must use the rules for Multiple Attacks and Two-Weapon Fighting. Note, Servo-Harnesses like Servo-Arms do not count as Multiple Arms. Therefore it is only Two-Weapon Fighting at best. Not 3 or 4 Weapon Fighting.