1. yes. It needs to include all the details according to Employer Job Offer pdf guide (hours, job description, duties, salary, vacation days etc).
2. look up minimum requirements for the employer on OINP website
https://www.ontario.ca/page/oinp-employer-job-offer-foreign-worker-stream#section-3
Revenue, median or above average salary for your NOC in the city you will work in, you need to have at least 2 years of experience, company needs to be in business for at least 3 years
3. No until you have signed employer form from the employer. When you start application, you need to submit all the documents within 14 days. Otherwise they'll delete your profile.
4. If you are not currently in Canada and don't have valid WP, I believe LMIA is required. (have no idea how it works for outland applicants, I'm currently on valid WP in Canada and LMIA wasn't required)