Is it strictly a case of one or the other? Why couldn't you find part or full-time employment in an area that will develop your skill and dedicate the rest of your time to applying what you learn to building your startup slowly? Going full-tilt may be exciting but without savings, it can be diffi...
Everyone does this. For example, take the entire LAMP ecosystem. You could write your own Linux + Apache + MariaDB + PHP + OpenSSL + WordPress... Or you can just use these, as they currently exist. Same applies to ideas. Dan Kennedy is found of saying, "Pioneers come back riddled with arrows...
Yeah, you have got this right. One important thing to note is that you will need to add href lang tags on the pages for both apptamin.com and apptamin.ca. Certainly no need to use canonicals based on what you have explained.