I'm certainly not an expert but will attempt to answer your questions with some quick comments. I'm sure there are other people out there with complete answers.
#1 Try Dave Naylor's site www.rcskydiving.com
His equipment is used by many and took all three places at the Muncie 2006 Rally in September. Used two small jumpers hauled up by a small electric jump plane. And third place with his "Advanced" jumper
#2 There are plans on the web, I think Juan has some of Wally Gitchell's canopy plans and some are available thru AMA's plan service.
#3 Jumpers are usually carried with a jump box installed on the bottom of the fuselage and controlled by a servo operating a release pin. Also, jumpers can be carried by pods mounted outboard from the fuselage and using servos to release the jumpers
#4 I'm only familiar with the larger jumpers, 60" span and weighing approx 3.25 pounds It was my opinion that the larger jumpers "fly" better, but Dave Naylor's jumpers certainly disproved that theory by using a superior design. Weight is dependent on the size of the canopy and the need for good penetration when the wind increases.
Hope this helps some