Hey welcome I'll try to answer your questions as best as I can.
1. Factions can use any model in their faction. The only restriction there at this time are some totems are bound to certain masters. 90% of the time your list has to stay in faction. There are some models that allow the taking of out of faction models however.
2. The factions are nearly that focus'd imo. The guild have hard counters. The ortegas shoot really well, Lady J is an anti undead machine, and Sonnia is an anti magic user caster. Out of the guild LJ is the combat master. There is no shooting faction, melee faction, magic faction they really can do almost anything.
3. A standard deck of cards works you just need the little guide. The suits correspond to different suits in malifaux. There is a quick reference guide stickied that is great for that.
4 and 5 fall together it's pretty unique. Not sure who coined it but;
"I'm often asked what genre and elements make up Malifaux ... that's simple, its: Steamvictoriohorrorwestpunk! Hope that clears it up for you." is a common line.
When doing terrain (there are rules in the book) the location chosen/random'd could be any number of places. A swamp, gremlin village is going to look much different that a wild west prairie town. It's a large area that is filled with different themes.
Hope that Helped,
Ryan