1. Only Ministers may introduce legislation (unless on an Opposition Day, see below). This way there is a clear government program and clear debate between government and opposition. I, for one, tired of the lethargic debates in the Atlasian Senate that strove to find consensus among everyone. That might be nice in the RL, but it's good to have some solid opposition in a game.
As Hagrid alluded to, the usual division of bills in the Westminster System is between government bills and private members' bills. I think the standing rules is that all legislation proposed by Government will be introduced in its own topic. There should be another topic in which all private members' bills must be introduced, then the Speaker can decide if/when to introduce them.
Do you really want to make the system so formal? Since our game doesn't really feature substantial executive business, I don't see why people can't just speak up during a Questions thread.
It would be good to have a thread like this, so long as we enforce that zingers and complaining go there while serious discussion about bills stay in the legislation threads. In other words, the Questioning thread ensures the legislation threads don't get clogged up.
Speaker or leader of the house? Which motions in particular? In general we want to set the rules so that bills that aren't successful will be voted down rather than amended constantly. This is where a "First/Second Reading" section may be useful.
You'll want to set time limits on this too, maybe once every 30 days.
I have no problems with 2, and my problems with 5 are the same as everyone else's.