Lots of good advice here, but the most important point has been missed. In CivII, you must expand or die! You cannot co-exist in peace with the AIs. Eventually, as you become more and more powerful, they will turn on you, especially in MPG, so, you need to acquire AI cities at every opportunity. Early on, this may mean by capturing them, than, as your democracy takes off, buy them! Use dips/spies to buy everything in sight! This will provide you with none units to garrison your cities (note: I consider a none unit too valuable to waste in an offensive mode), and will make the AI cities your cities. Yes, you will have to pay double to avoid an incident, but its worth it. As long as your trading, you should have plenty of gold to buy cities. Remember, you cannot live in peace with an AI for long, so your long-range goal is to reduce all the AIs to one pet city while you build and launch your spaceship. Keep those vans moving and you will maintain your tech per turn as well as having plenty of coins. The best defense is a good offense and a spy with a few bags of coins is much more dangerous than several vet cav units.
Keep your reputation spotless, and, after an AI has sneak-attacked you 2 or 3 times, your senate will support further "peacekeeping activities" against that AI. Done properly, the only cities you should have to attack in a democracy are the AI capitals.
Regarding the OEDO trick, remember, you can switch govs as many times in one turn as you like, so, revolt, pick a fighting gov, Monarchy, Commie, or Fundy, blast the AI target cities, than, on the same turn, switch your gov back to Democracy.
From your post, it looks like you are on the right path, you are just not expanding enough, oh, and don't choke your cities with a bunch of defensive units in democracy. You only need 1 and if you don't have a none unit available, you can use a van or dip/spy in a pinch. And with a lot of cities, if your really must go on the attack, each city can provide one attack unit without choking it or causing uncontrollable unhappiness. Especially with the right wonders...!