OK, I will field at least some of these.
1) The first civ to discover a religion's "Enabling Tech" gets an opportunity to FOUND that religion-with a city automatically becoming the 'Holy Capital'. The founder can then passively or actively try and spread his religion to neighbouring civs-and try to encourage other civs to adopt that religion as their State Religion (which is covered under the Religion Civics).
2) According to the developers, there will be scenarios shipping with the vanilla game. Plus the game will apparently come with FULL modding tools from the outset (and MP!!).
3) How do you mean? If you mean SMAC-style, then the answer is NO I'm afraid. However, land and sea units can earn up to 41 different promotions, thus allowing your units to become 'ultra-specialised' in a variety of different ways (like specialised city defenders, or units which fight best in forest/jungles).
4) Hard to say exactly, but I would say the tech tree will be LESS complicated than in civ3, largely because you don't require all of a techs prerequisites anymore. This allows for greater flexibility in how you progress through the tech tree. Also, strictly delineated Ages have been removed.
5) Too many to list in this post. Might I suggest you check out the Civ4 Pre-release thread started by Civrules. This shows all known Civs and all known leaders.
6) Trait system has been retained. However now these traits (and, I am assuming, the civs UU) are associated to the leader of the civ-not the civ itself.
7) Unfortunately this is the one I can not give a good answer to, because we have heard so little about this facet of the game. What we do know, though, is that AI leaders now have specific personalities and agendas a la SMAC. This will hopefully make them much less erratic to deal with in diplomacy. We also know that you can negotiate 3rd party peace deals, or start 3rd party wars, without direct involvement in the conflict yourself. Lastly ALL resources (bonus, luxury and strategic) are tradeable.
Anyway, hope this helps you in your decisions in relation to Civ4.
Yours,
Aussie_Lurker.