20 cattle would be overkill. I'd have 7 settler factories pumping out settlers and workers like no tomorrow!

BTW, you wouldn't be able to use those 20 tiles until you get hospitals.
Ok, some basics:
1 - "Mine green (grassland), irragate yellow (plains)". Exceptions: You can irragate any food tile (cattle, wheat, game, wines, etc.). Don't settle on a food tile. Unlike Civ2, you'll lose that food bonus. Despotism also has a food penalty, so irragating grassland (without bonus tiles) doesn't have an effect. (same for mining a cattle on plains - already has 2 shields).
2 - Never automate (this includes governors).
3 - Always trade. Also, keeping the AI at war will lower their trading, thus keeping them behind you in the tech race.
4 - You only need 1 defender per city, and 2 defenders in your border cities.
5 - You don't need every wonder and improvement in the game. i.e., you really only need walls in border towns, and at that, if an invasion/war is emminent. Coloseums are really expensive, and you don't need them unless you lack the luxuries.
6 - Use the lux slider instead of entertainers. That way, you don't waste shields.
7 - Never attack across rivers. They give a +25% bonus to the defender.
Also, read up on the strategy guides. It's a great place to find info. (Remember that some may be for vanilla Civ3, PTW and/or C3C).