I was in the original and I am a good friend of the OP. I can probably answer some of these.

1: Yes. Just... try to be stylistically similar. No robots, no aliens in space ships. Something that fits the world we are in.

2: This is tricky. The best way to handle it is A: Be vague when mentioning specific nations, B: Try to only directly interact with players or NPC nations that neighbor you directly. C: Even if you travel, ignore as many details about the wilderness as you can get away with.

3: Presumably there are pre-existing relations. I would imagine there are translators for your neighbors wandering around, and there are translators for the more active trading powers. 

4: Don't worry about numbers. I don't think having population and army number limits are conducive to anything. Same with the rest. We are RPing over a relatively short period of time, so you won't be moving up a civilization style tech tree. Tech improvements would be slow and subtle. Maybe the Dread-Engineer Broseph discovers a new crossbow and brings it to the court of the local ruler to show off. And, impressed, the ruler orders a few hundred built. That would be how technology would play out. Nobody wants to see some in-RP conversation that goes like this.

Steward: "Mi'lord, we have reached level 15 in the weapons tree! We can now use shootin' guns."

King: "Excellent, Steward! Next we should research on the social tree. I want us to discover prostitutes who don't have the pox."

Pretend you are writing a book or a tv show, not like you are playing a game.