I'm working on the guillows spitfire 27 5/8". Geared speed 280. go to this link for info
http://rcmicroflight.com/library/convert.asp:
His set up for mounting the motor is sweet. Although i was not satisfied with styrene nose cone so I used it as a mould, poured in some plaster of paris, put a stick in it to hold onto. Then get a plastic pop bottle (stronger plastic) jam your plaster in there and shrink with a heat gun. I found that Evian water bottles have very light plastic and are very flexible. This setup should reduce damage in a crash. I used the supplied plywood firewall glued to nose cone, hole cut for motor, made a shelf where motor stick thru and strapped her on. I'm thinking sheeting the entire plane would be too heavy. speed 280 geared would allow a weight up to about 14 oz my research would say. My spit is coming in at about 9 - 10 oz. Ithink you might be able to go more power because of strenghth of sheeting, but will it fly? let us know how it's going.
As for matching speed controllers surf.... lots of godd info out there. ESC's are rated in amps. 5 A is good to speed 280 but direct drive you might burn it. learn the formula ; watts (work done)= volts(potential pressure) x amps( current or how fast the electricity is flowin). so if you have 5 amps limit at 7.2 volts you get 25.2 watts of work. thats direct drive. change prop sizes and you will increase and decrease amps. change volts and the other variables change.
Now add gears. since a motor is max efficient running full out, a gear box allows this but slows down the final shaft speed. ththen you can put lareger props with more pitch on, get more work done(watts) and reduce amperage (current = heat= burn)for the same volts. used this fornula and play with it plugging in variuos values until you get it. Then look for other people combos and values. I read in the article mentioned above that his 3.5:1 geared 280 with a 7x6 prop got (his math seems wrong cause 8 cells is 9.6 volts I think) 3.25 amps and 26 watts. 26 / 3.25 = 8 volts? any way, increse volts with same prop and amps go up. same volts smaller prop amps go down. play and learn