Ok, lessee if I can answer some of these...
1. You CAN start with multiple cities if you really want to, but I think it's rather a waste to do so, as you'll end up with just a bunch of really scattered buildings if you do that, and for your first city, you want to get it up and fully running ASAP for best results, so using all 9 action points on the initial city is usually going to be the best idea. And if done right you'll have some extra rock/wood and stuff fast anyway, so you can set up another town center within just a couple of turns if you really want to.
2. Yep. It's more important on Hard and above, in the current beta version with the specialization, but even on Normal or Easy (in any version) it's still a good idea. Particularly after the recent changes to military unit costs, it's now a bit more difficult to have multiple types of military buildings in one city because they then each require a bunch of seperate buildings to keep their production going. I often find that designating one city as "barracks only" or "siege only" can be very helpful for this, and can make it easy to increase the number of military buildings of that type in the city by keeping some free space open. But even for resources it can be a good idea at times. Try a city that's mostly just clay and incense production, and add an Artist's Studio onto it for a huge boost.
3. Yeah, this is a useful thing. Particularly when you're dealing with the more difficult to get resources, it can be a good idea to have specialized "resources only" cities behind the front lines, preferrably near other cities that are pumping out military units so that they're protected. Again, this is even more important when resource specialization comes into play.
4. No. There's no point in spraying land tiles all over the place unless you see an immediate strategic need for them. When you decide it's time to expand and make a new city.... THEN you should start dropping some tiles leading to the spot you want to place the city. Generally done as "land bridges" that simply lead out to the proper spot; takes just a couple of turns to set up, usually But doing it all the time? Nah. The landmass will grow quite nicely on it's own.
5. Not really. Theoretically they're not a terrible idea, but there's not too much benefit to doing that either.
Hope some of that helps. If you can think up more such questions, I'll try to answer them as best I can to.