You can set up your express entry profile. It determines what you are eligible for, you do not pick whether it's FSW or CEC.
You will be ineligible for a FSW application until then.
LMIA is a closed work permit.
Yes and no.
If you have an LMIA, you probably don't need it, if you qualify for the CEC class.
If you want FSW class, you need it.
Yes it is a points boost, but is a requirement for FSW class.