@kflorian and Propunk - Hi guys. I play on my Noble myself and I'm still on my first game (using the Total Realism Earth map) as England (Elizabeth). I can't tell you any real good tips, since I'm still kind of feeling my way through myself, but I can maybe give you a little help from my own experience:
1. When you think you have enough units for defense (probably 4 or 5 units per city), and if you can't build anything else, then hit Alt-M and lease out your units as mercenaries. Best case, you find a willing taker and make a little cash upfront and some every turn. Worst case, you don't have to pay maintenance for the units (but you have the advantage of being able to recall them in case of emergency, allowing a 2-3 turn delay). I understand that mercs will be tweaked in the next patch, though, so you might not want to learn any "bad habits" that you'll have to unlearn later
(Of course, I'm assuming here that ALL of your land that your cities can work is developed to the limits of your current tech. If not, then build a worker/military-unit combo and get those improvements up ASAP - especially gold/silver/gems).
2. In my game, I only founded 3 cities (2 in Britain, 1 in Ireland) for a LONG time. I picked up my 4th city (Oslo) by taking it from the barbs around 500BC. Then, I didn't expand at all until I had Astronomy (around 1200AD) and could send out galleons to take barb cities in southern Africa and the Far East. It's now around 1600AD, and I've got about 17 cities scattered around the globe and am in 1st place in points, about 600 points ahead of 2nd place. Remember, it's a marathon, not a sprint. You don't need a lot of cities early. You can always build up your military/economic strength and then explode peacefully/militarily at a later time.
I hope that helps a little. It's a great mod - especially with the rebalanced civics and the way tech spreads - so stick with it. If you're anything like me, it'll grow on you after a while....