I'll try to write a bit about the situation with the Monaco fans and their attendance.
The original Stade Louis II was built in 1939. The capacity then was 12 000. The stadium got demolished in 1989 to replace it with a new one. The current stadium has a capacity of 18 500. According to wikipedia, in 2011 the population of Monaco was around 36 000.
Las two times ASM won the Ligue 1 were in 1996/97 and in 99/2000. During 97, the average attendance was around 6000, in 2000 it reached 10 000. After that, for few season the average attendance remained as low as 7000 - 8000. It only got up to 10k after the 2003/2004 season (CL final). The numbers began to drop few seasons before relegation. Their last season in L1 was also a failure in crowd numbers. Average attendace didn't even reach 7000. Other teams relegated that season were Lens (avg att 31 000) and Arles Avignon (avg att 9000).
The first season in L2 was even more embarassing for Monaco - the average attendance dropped below 5000, while Lens kept getting around 30 000.
This year, after all the spending, the first home match against Montpellier had over 14 000 specatators, which is a pretty good ammount of people, I doubt they can keep the momentum, but most likely they will get over 10 000 in average after the season is over. By the way, 10 000 people also came to watch Leicester City host Monaco during the pre-season, in July.
The biggest fan group for ASM are the Ultras Monaco 1994. Inferni Biancorossi, also started in 1994, dissolved in 2010. In 2003 another ultra group was formed - Groupe Heracles 2003. I don't even know if they exist anymore. Few years ago, they were the most active of the fans when it came to away trips. At the best of times, the ultras have occupied one or two of the stands at Stade Louis. As far as I've heard, the hardcore supporters of Monaco haven't really gone along with the political polarization (e.g Marseille ultras are left-wing, PSG ultras are far-right), but they do tend to be rather right.
There's also the official Supporters Club, who organize the ticketing for away matches and try to cooperate with the ultras (e.g try to avoid conflicts like the one that resulted the club being punished last season).