You might not need to cut at all before starting your dreads. It totally depends on how damaged your permed hair is.
umm why backcomb? why not stop combing give it a month and see if it starts to dread?
the best indication of if it will caise a problem isnt if u break off every hair on your head backcombing its if it will or wont dread on its own
once it dreads on its own then u will see if the permed pasrts ave a diferent texture and feel and u can decide if the permed parts should be cut after u already are dreaded
twists they twist way way too tight if its gonna break it will break while twisting it instead just take out the corn tows wash it shake it outr and let it dread
u dont need to do a thing to dread
just seperate if they try to join togerther
then when its dreaded u can see if the new growth textures too drasticly diferent or if they feel crunchy or weak
but id imagine its fine and u wont notice the texture diference unless u look really close
Please don't get your dreads done professionally. Locticians rarely know what they're doing and will destroy your hair. Just take some time to read up on things around here, ask questions, and then when you feel that you know what to do, find a good friend to help you start your dreads.