1, The 777 has a super-critical wing (i.e the wings thickest section is further back from the leading edge than normal.) This delays the onset of drag caused by the formation of shockwaves. Then exact answer..i dont know. I guess the weight saving from the lack of tips (even the cost saving) is more of saving then having them on. Plus, being a large wing there may have been a constraint on the span for parking at gates, etc.
2, 3 i think. Same as a classic? Pressurisation can still me maintained with one operating though.
3, Well looking at the overall picture, the loss of the trailing edge flaps would be the most limiting. These devices create a greater amount of lift than the leading edge ones. This reduced lift leads to higher speeds required, which leads to longer landing rolls.
4, A340? well in any plane i think the loss of one Hyd. System will cause no great dramas. Depends's on the level of redundency built into the aircraft. Boeings are great in that respect...dont know about the buses. Loss of 3 of the 4 systems would leave you with primary controls and items that were run from the existing system.
5, I think they are both fundamentaly the same. But i dont know.