My biggest problem is settling enough cities. I find the maintance cost too crippling to overexpand plus I try to optimize each city's placement (at least 1 resource, no cities overlapping which means cities have relatively a big distance between them). I aim for 4 cities before AD which I usually accomplish. I've built around 13-14 cities in total while the AI had around 30 (BetterAI mod). I usually play on large-huge-bigger maps, enjoy isolation (it fits my slow expansion) and sometimes succumb to my wonder-religions lust
My questions are:
-Should I go for land optimization or city optimization? Try to fit more cities or build better cities?
-A general guideline as to how many cities I should go for?
-Is city micromanagement necessary past noble?
-Can you support a big empire early in the game without a religious economy and with minimal wonders and still be compatitive?
I usually win on noble (not as consistently now with Better AI mod) but really dont know how some guys manage on higher difficulties...I tend to lose focus as my game progresses. Later game tends to become a worker/city micromanagement hell
First of all, don't be afraid of overlap. For most of the game, especially the crucial early game, your cities will not have enough population to work all their tiles. Later in the game you can compensate for the overlap with things like Sid's Sushi to give you enough food to grow the city. Overlap will reduce maintenance, and sometimes overlap is necessary to ensure that all the best tiles (like riverside grassland and flood plains) are within the workable fat cross of a city. Finally, one of the best things about overlap is that citizens from one city can work another city's cottages, ensuring they grow, even though the first city doesn't have enough citizens to work all of them.
On that note, since you're playing on Noble, I assume you're running a cottage economy, and that's the key to making your early game viable especially in the absence of an economic boost like a shrine. The key to the cottage economy is to be able to grow your cottaged cities as large as possible so you have as many citizens working and growing cottages as you can. Try to snag early happiness resources (gold, gems, silver, ivory, fur), go for Monarchy and Hereditary Rule ASAP, allow a religion to spread to you and adopt it and spread it for the +1

. Other priority techs are Pottery to be able to improve tiles with cottages, Sailing for trade routes along coast and rivers, Writing to open borders for trade routes, Currency for markets and +1 trade routes, Code of Laws for courthouses.
One other tip with cottages: the best cottage cities are near lots of rivers. Riverside grassland or flood plains are best for cottages as they have +1

to begin with; put a cottage on that tile and it automatically yields 2

--so it's as if it instantly grew to a hamlet. If you play as a Financial leader, a riverside cottage yields 3

out of the starting gate, so it's like getting an instant village!
Specific answers to your questions:
-Should I go for land optimization or city optimization? Try to fit more cities or build better cities?
A bit of both. Sub-optimal cities may be necessary to claim an important resource. Generally though, in the early game when you have few means of mitigating maintenance costs, you want the best cities possible. Hold off on founding sub-optimal cities until you have better means of making them pay for themselves.
-A general guideline as to how many cities I should go for?
4 to 6, generally, before you have techs like Currency and Code of Laws to be able to afford more.
-Is city micromanagement necessary past noble?
Oh heavens yes! Even more so, especially when doing things like optimizing whip overflow.
-Can you support a big empire early in the game without a religious economy and with minimal wonders and still be compatitive?
Yes--I hope I answered this question in my advice above.
