1+2. Bounce waving sucks for the most part. You'd have to ask others for numbers, I hate doing it that way. I imagine bouncing works well because it can be done out of fort stance, so there's that.
3. Gold is really good and underrated. Just know that it's not merely a passive dragon, and two very key buildings affected by Gold are wt and td. Emerald is not so good if you're using it for passive effects, but fairly good for aggressor kingdoms - use it to inflict extra kills on your initial wave, and if you force a tank it's great to force enemies to chain into -15% gains early war. Many kingdoms will tank an Emerald though, and you don't want to fall into a trap of lining up your attackers to all be bloat hogs and useless too soon, so if you throw Emerald and can force enemy to tank, it helps to target t/m or strong defense provs, even if it looks like slower damage in the short-term. Sapphire is highly overrated, even against cow kingdoms, just because of how random ops are, but if none of the other drakes are relevant then it's okay - just don't rely on it as a defensive dragon, and Sapphire is best for kingdoms with a general wpa advantage already. Idk when ruby became less popular, since it's the easy default dragon... pretty hard to mess up -8% ME.
4. It can be marginally better than FB per-cast, but it's most useful for holding a tough FB target until someone else can finish balling. It also blocks the birth rates of any kidnapped/landgrabbed peasants, so pretty useful.
5. In war? Build homes if a chain is imminent, or you are one of the first chain targets and going to go down deep. Otherwise they're pretty crap, but sometimes it's better to keep some homes/peasants going into war than to remove all of them.