1. you can still apply OUTLAND even if you are living in canada on a work permit. if you have a current valid work permit, then there is absolutely no reason to be applying inland, especially if you happen to be visa exempt. if that is the only reason why you are applying inland, then i would highly recommend reconsidering. most outland visa offices approve applicants in 6-12 months. most are approved within 8-10. can you even apply for an OWP when you currently have a valid one? i would recommend double checking that. also, it's still not guaranteed that new applicants will receive the OWP in 4 months from when your application was SUBMITTED.
2. the marriage certificate is a REQUIRED document, and must be submitted upfront. not submitting the marriage certificate upfront risks delays in processing, even getting your application returned. it is not the same as not submitting your medical or pcc upfront.
3. if you don't have any criminal or dependant issues, then there is no need to waste money on an attorney. many give out wrong advice, and all they are really there for is to "double check" your paperwork. if you are a competent human being, then there is no need to pay someone to "check" your application.