You might want to check out the following web sites
The official Armati web site with an explanation of the current rules and their mechanics byt the author, the army list creation formula, lists of armies, FAQ and other things.
You don't have to join to read the messages.
Now to your Q's.
(A)What are the basic rule mechanics of Armati?
Really best explained by the author on the official site.
(B)How many figs are in units?
As Billiam says troops are placed in categories or types like other rules FT = heavy foot SI = Skirmishers HC = Heavy Cavalry...and so on.
Figures are based on stands of 1 model and 2-4 figures just like DBM - using the same size stands. So, 4 HI to a 40mm x 15mm stand in 15mm and SI would be 2 figures and HC 3.
As Billiam said there are three scales, into, optimal and epic. Units are formed of 2, 4 and 6 stands respectively.
(C)How many figs are in an army?
Depends on the army and the troop types in it but you can start at the intro scale and work up and Billiam's numbers are the right ballpark.
(D)What do you think of them?
Personally, I love them, most regular players do, other people favour other rule sets and their views of Armati will correspond to a range of views. But, if you've looked at all the others you mention and not liked them then Armati may be your thing.
I would suggest looking either on the Yahoo group or the official site for a club where Armati is played and then arrange a game or two with an experienced player at the intro level. Armati players tend to be a relaxed bunch and willing to coach new playes through their first few games.
(E)Are there any good Armati websites?
See above. There are others and some are linked through the links section of the Yahoo group site.
(F)What is in Advanced Armati?
Aaah, essentially a set of optional rules that were added to Armati to provide additional enjoyment. Now, most of us play advanced Armati.
But, not to worry! The new version of the entire rules and lists...Armati II rules including the advanced stuff and 130 lists...is currently being printed for distribution as you will see headlined on the official site.
All the Best