Ok, here's a few answers which I hope will help:
A) Yes there is... Muay Thai shorts must give you freedom of movement to allow you to kick unrestrictedly. This generally means allowing for plenty of room around the thighs and hips.
B) see above + light breathable fabric (satin) + good elasticated belt
C) Twins, King, Tuff, Kombat, Lumpinee ... lots of choice out there
D) They'll last for years, but you can usually find bargains for $15/$20 if you look hard enough, and the design is not all that important to you. Check out
MuayThaiStuff.comE) As far as I'm aware, most Muay Thai shorts will be made of satin. But I think you might also be able to find silk ones, which will be lighter, albeit more expansive, and not as durable.
F) No preference: whichever brand my club orders (as it features the club logo), but again, check
MuayThaiStuff.com for bargains, and a wide variety of designs.