You need not apply for an FM3 (you can buy property with it) until you are in Mexico and have an address. The exception would be if you are going to ship household goods on a 'menaje de casa.' That would require getting an FM3 within 90 days of your entry into Mexico, registering it when you arrive at your destination and within 30 days of crossing the border.
You'll need a response from an experienced Canadian expat for the questions which relate to Canadian rules.
Be sure you want to live on the coast and experience the oppressive 'hot & humid' for much of the year before you decide to purchase property. Many northerners find that climate intolerable through the summer and fall and need to escape to higher ground and cooler climes in Central Mexico. Maintaining two seasonal homes can be both inconvenient and expensive. We find it better to live in 'perpetual springtime' and go to the beach at the appropriate season for a mini-vacation.