Yes.

EDIT: Long answer, you can through the casus belli mechanics in game. As a civilian you can overthrow an existing Count but doing so would be incredibly difficult for obvious reasons.

iirc You can also be awarded the Count title by a King should say one of his current counts proves to be a traitor and you prove to be worthy as a replacement.

More info can be found in this Dev Journal here

Yes, you can earn nobility in-game without IRL money. I believe you will have to earn something called 'story points' to be able to gain a title.

Yes you can. Not every noble is going to be able to hang on to their position. Some will foul it up and get thrown out by their subjects. Or some my decide they do not like the responsibility of being a noble (yes you will have tasks to do to take care of your lands) and just abdicate. In which case a new count, duke, or even king will have to rise up and take over. where will these come from, from the rest of us, how it will work we will see when it happens. Just because someone bought into the game as a noble doesn't mean the get to keep the position. They have to earn it and some just will not be able to hack it.

Yes, in fact after launch there will be no way to directly gain a nobility using by paying money to SBS. The noble titles and positions being sold right now are more for setting up the world's during exposition, and having the initial nobility structure for the first few months of the game.

Sometime within 1 to 3 months after launch I bet we will see the removal of most if not all of any npc nobles, and possibly the first overthrows of human nobles.

I don't know about first year.....

We still don't know the level of skill regular guards have and thats not even thinking about the royal guards who would be the best fighting NPCs.

They would be at minimum of Master level of skill imo, but prob more....