While I find something of a disconnect between your questions and your profile ... the following is a brief and rather simplistic overview of the answers.
(a) severe turbulence gives rise to two concerns .. stalling and breakup due to excessive structural loads. The design standards require the OEM to provide guidance to flightcrew relating to recommended speeds in such circumstances. Engine thrust will be adjusted to whatever target is appropriate to the recommended speed.
(b) turbulence will cause time varying accelerations and pitching motions. The centre of pitching motion generally is somewhere near the forward half of the wing. As the rear seats are some distance from this region, accelerations due to the pitching motions may give rise to a perception that the turbulence is "worse" than might be thought if one is in a seat row closer to the wing.
(c) most jurisdictions regulate a minimum distance. Operators (and pilots) may well prefer a greater distance.