I would recommend leaving the drawing units well alone.

The symbol size that Quenten and Jim were referring to is this one - the Default Symbol scale highlighted below. Changing it will change the size of all the symbols from that point on, but will do nothing to symbols already placed in the map.

However...

Since you are saying that everything is too large is it possible that the map itself is too small?

Following Ralf's most recent Live Mapping Session demonstrating the use of the his John Speed City style, published in the first Cartographer's Annual, I did this map this evening.

John Speed had actually done a map of this town - my county town, so I used that as a reference for the approximate shape and form of my own map.

This is the first map I've ever done in this style, and I enjoyed it enormously.

I hope you don't mind, Ralf, but I decided to add a parchment texture overlay...

Oh dear!

But sometimes it's the way to go if you don't like anything about what's there.

Keep going...

(I can't do everything, but it would be interesting to see what people want)

That's interesting. I didn't know you could edit a poll!

And I would say it depends. Although I don't play myself I've heard plenty of people come down on either side of that argument for different reasons, ranging from "It's much easier to prepare", to "It gives the game an atmosphere from the start".