The best way in mount and blade to make money, no matter what module you're playing, is to loot & burn cities, and sell the loot in towns/villages. Whenever you loot a village, you get many valuables, such as raw silk, salt, wool, wine, pottery, etc, which is worth a lot of gold. You also got tons of food. I'm talking about 9-14 slots of delicious cheese, bread, meat, whatever you name! You can sell all of it at towns, and make a pretty huge profit from only a few villages. On the bad side, however, you will be at war with the faction, and while looting, you cannot move, so an enemy lord or patrol may attack you, and ruin your day. But hey, who said quick cash was easy cash?
Before the L'aigle patch of 1.1, this gave you a **** ton of money, but Docm30 has patched this in that patch. Still though, you make quite a lot of coin (about 1,500-3000 gold a village,)
Since you joined France (And may as well do it again) You should start off being at war with Britain and Russia, two good nations to loot villages in. Start off by recruiting half line infantry and half heavy cav/line cav. Recruit all you can, use all the money, since you don't lose money at the end of the week. You should have around 20 troops.
Now you have the choose. If you want to loot some British villages (I don't recommended this with only 20 men, i'll explain later) head up into Ireland, since their cities are very spread out. Loot one or two (depending on Inventory Management skill) and rush back home. I don't recommend this at first because if you get caught, you're pretty much screwed. It's very difficult to get out of the British Isles once you're in...
If you go into Russia, which is also nice, their cities are also very spread out. Loot one of the border ones next to Prussia (a quick getaway and towns are right there.) and sell the loot. Russia is also a much better option since you can safely move in and out of Russian territory very quickly, so it's a good idea to loot one village at a town, going in and out through Prussia and Russia, selling loot and looting villages.
Be careful though. With only around 20 guys, the villagers will come out and fight you. Now, if you only have infantry, you might as well just not even bother, since they will be destroyed by those peasants (strange huh?) This is due to the bugged melee system, which makes infantry pretty much useless when it comes to close-quarters combat. However, if you have cav, you will be saved. When the villagers start charging, move with your cav, and go around to their flank (behind them or to the side of them) Once the villagers engage, set the cav to charge, and just watch as the cav completely wreck those plebs, just as they should.
Anyway, after your first loot, you should have enough coin to recruit a lot more troops, which will in-turn make it much easier to loot villagers, which will make it easier to make more money, which will make your life a whole lot easier and your experience a whole lot more fun! After looting maybe a dozen villages, if even that, you will be set, with around 50 or so ranked up troops. You're now ready to take on the world! Fight a few enemy lords along with the other officers of your chosen faction, or hey, loot some more villages. Why not? The world is your oyster!