sennadog I think that I have previously come across a possible answer to one of your questions:-
1) A pilot in the RHS, who holds either an IMC rating or a full IR, cannot legaly fly on intruments in IMC, UNLESS:-
Either, the aircraft has a FULL duplicate set of instruments & navaids, in front of the RHS.
OR, he also holds an intructor's rating
I understand the logic to be, that it is dangerous, for the pilot in the RHS, to try on fly on intruments that are only in front of the LHS, because of the parrallax due to the offset line of sight. Instructors can, as they have been trained to allow for this.