I am in same boat.
30# and 40# refer to draw weight at the std draw length for the bow. Not sure how that is determined.
Brace height I believe refers to the distance from the bow handle / arrow rest of the string at a rest position. On a recurve this is a function of how tight / loose the string is.
AMO is a standards org that defines size of bow as string length plus 3 inches.
Taking a lesson tomorrow on a recurve and getting set up with a new bow tomorrow.