I'm a little curious about this one. When you say a ceiling fan, you literally mean the thing that hangs from your bedroom ceiling, about 4 foot across?
I'd be curious about the strength of the actual unit itself, especially if you're taking something that's meant to hang from a ceiling and using horizontally. Its bearings work on an almost entirely axial load, a horizontal wind turbine usually uses something like a tapered roller bearing, allowing it to deal with both axial and radial loads. Usually you can get away with something a little less suited, since its only a small unit, but I would still question the use of a ceiling fan. Something like a pedestal fan would probably be more appropriate.
To answer your questions, in my opinion:
1: Nothings a waste of time if you feel that what you've done was worth while for either practical results, fun in building something, or serving as a learning experience. But, I doubt it would work real well.
2: More magnetism does lead to more power generation, but, then you're putting greater load on your turbine. In a purely theoretical sense, it doesn't really matter, you'll get the same generation since you'd be spinning faster with less load for the motor to fight against. For a motor with a magnetic field perpendicular to the direction of rotation, the general former for output voltage is emf = vBL with v being your angular velocity, B being your field strength, and L being your rotor length. You can only create power by inputting an equivalent level of power, this is the conservation of energy principle. As you increase your magnetic field, B, you'll have to fight harder for your magnetized rotor to cross the field, meaning you'll turn slower, still giving you roughly the same amount of power. If this wasn't the case, everyone would just chuck huge magnets on little devices and create a heap of power. The best option is to play around with it a little and check your efficiencies. I'm guessing you're not going to be precision machining this device with special engineered materials, so, you want to keep your rotational velocity pretty low, that way you don't have to worry about over speed on bearings, things flying off, etc... So, put a magnetic field around it that allows consistent generation, without the unit having to spin too fast.
3: For your purposes, it doesn't really matter.
4: I've made wind turbines before, but I've not built one from a ceiling fan, but, what I said in the first paragraph says what problems I'll imagine you'll come across.
5: A ceiling fan is an electric motor. Any electric motor can be a generator, and any generator can be a motor. They its just whether the electricity is applied to create a movement, or a movement is applied to create electricity. The thing to look out for is whether you're using an AC or DC motor. A ceiling fan will almost certainly be AC. You'll need to convert this to DC before you can feed it into your battery bank. You'll also need a charge controller for your batteries to stop them from back flowing into the turbine and turning it into a motor, and to prevent over/undercharging. You can buy units that'll do this for you, or you can make them yourself. To convert AC to DC you'll need a bridge rectifier, which is basically 4 diodes arranged such that a positive signal is always generated, however, it does still vary in amplitude, so you'll need to use some capacitors to level the voltage out to a nice smooth output. Then you'll need to use some filters and whatnot to make sure you're charging your batteries at that oh-so-sweet 13.4 volts that they love so much.
I hate being the kill-joy for people's ideas, but, in my opinion, it's more work than its worth. If you still want to give it a go, by all means, do it, it should be a lot of fun, and I'd be keen to see some photos/video of it in operation. However, for simplicity, you can't go past a solar PV system. They're so much easier. There's no moving parts, and they require almost no maintenance. You'll still need a charge controller, but you need it either way, and if you compare the cost of a PV system versus the cost of trying to modify this fan, its probably going to be cheaper to go the solar route.
Let us know how you end up going with it.
