vaulted with 'loft' info needed

some background to my situation
-my home is 1950's construction
-single story
-24'x24' floor plan
-load bearing wall in center runs from gable-wall to gable-wall
-gable roof
-roof dimensions rise of 6' run is 12'
-2x4 ceiling joists 16" on center 12' long, they rest on load bearing wall then another 12' long joist running the other half of house
-2x4 rafters 16" on center
-ceiling joists are not nailed to rafters they rest in between each rafter but are nail to exterior wall top
-2x4 collar ties at 2' below ridge beam, 8 in total, evenly spaced
-1x6 ridge beam

what i would like to do:

-remove 11 of the ceiling joists that run from exterior wall to load bearing wall, exposing a ceiling area of about 200sq. feet
-then i would like to sister 2x8 to all existing ceiling joists to create a strong floor for the new loft area, which i have now exposed
-sister 2x6 to all rafters
-raise collar tie up 12" (hopefully) and use 2x8 for this
-add plywood peak triangle tie as well

do i need to add a few ceiling joists to the area i removed them from to help with the roof, maybe use 6x6 or beefy 8x8's, lets say 3 of them???

or will the beefed up rafters and collar ties as well as remaining 400 sq. ft of existing ceiling take up this stress?