Wow - two for one in this thread. So debate 1 - REX and how many cities. I love to hit double digits by 1 AD, but not always possible. When I was moving from prince to monarch, I played a game to test myself, where I was isolated, and my capital, once at size 5, built nothing but workers and settlers - I wanted to see if I would run out of money or out of land first. I ended up with the entire island filled, with about 25 cities, overlapping everywhere, at some point in the 500-600 AD timeframe. Was still turning a profit at like 20-30% tech.
Then, obviously, with some economy techs, maturing cottages and meeting other civs, I got up to 60% and was producing obscene numbers of beakers. It was a cakewalk from there. I found it a good way to demonstrate the power of getting more cities and land. As long as I'm not losing money at 0% research, I continue to try to expand, because I can get out of that hole and will be better for it in the long run. That's my rule of thumb. Some will say you can be losing money at 0% and be fine, but I'm a little too risk averse than to try that too often (although I have been in that situation in the occasional Mongol keshik romp).
Debate 2 - regarding monarch being a novice level - it may feel like that to many of us now, and to me as someone who's just now trying to move up to immortal, monarch does feel easy. In fact, I just won my first monarch OCC the other day, and that was actually even relatively easy. But, I've now been playing civ for a little over a year. The first couple months, before I found this forum, noble was a struggle - I considered those my "novice" days.
Once I found this forum and starting learning the game, after a month or two of learning, I started to crush noble and prince and made it to monarch, where I was for a couple months while I practiced and got better and better. So I would think of monarch as an intermediate level. Frankly though, I'm willing to bet that if there are people who aren't on this forum and are active players of the game, very few of them would be monarch players or better, because it's the collective learning we all share that make us better players and allow many of us to be at the higher levels. So I would tend to agree with others who think of monarch as an intermediate level - to me noble is a bit more of a novice type level, one that people will quickly move up from once they spend a few days on the forum or a bit of time practicing the game.
An interesting poll question would be "What level were you playing at when you found this forum?" If more than half answered monarch or better, I'd be surprised. People on this forum are bound to be on the higher levels, because if they're smart and pay attention to other's games, they'll move up just based on osmosis.