1. Is there a way to reveal the map without exploration? Can I trade maps with the other factions? It would be nice to know what's going on in the rest of the world without actually sending someone over there.
Kinda an exploit way to do it - buy a hundred or so bands of eagle eye and equip them all on one hero. It'll reveal a huge chunk of map. Apart from that you can either use the reveal spell constantly, or send out explorers.
3. Is there a win overview? I have no idea who's winning or how.
Define winning. You've got four possible win conditions:
1. Conquest (defeat all other players)
2. Diplomatic (Ally all remaining players)
3. Magic (research and cast the master spell)
4. Adventure (research and complete the master quest).
1 & 2 should be easy enough to judge just by looking at diplomatic relations, the strength graph and the map. 3 is harder to spot, you could check their cities and see if they have any of the higher level magic buildings, in which case they've been researching magic but beyond that ... 4. is slightly easier because you'll see the new sites and higher level spawns whenever anyone grabs an adventure research tech, but of course there's no way of knowing which line they're pursuing.
4. What is the purpose of Charisma for champions?
Nothing as far as I can tell
5. How can I send a caravan to an ally's capital city when every time I right-click it opens up the diplomacy screen?
You need permission to wander their lands (non-aggression pact at a minimum). You can right click on any part of the city, not just the centre, or even move the caravan in manually with the keypad.
6. Do open tiles increase when a city levels up? The whole open tile thing confuses me cause there appears to be lots of space. Is there a link or discussion thread that explains open tiles in detail?
Nope, you get fifty slots maximum. It shouldn't be a problem as long as you specialise your cities rather than trying to build everything - note that the +% buildings have no effect if the city isn't creating that resource in the first place, and if you're only generating one point of that resource building all the economic buildings still results in less than 2 of the resource being generated.
7. What is the meaning behind 'likelyhood of being available' for techs?
Whenever you complete a level of research you can choose a tech to unlock. The likelihood is their chance of appearing here, if it's green you'll always have the option to take it, yellow or red and it will only sometimes appear. If there's nothing left in that branch of tech but unlikely techs you might need several levels of research before they appear.
8. Why isn't there a simple tech tree like in galactic civilizations/civilization/etc? How am I supposed to plan anything without it?