in short: you need a good GPA, a good LSAT, to go to a good school, not mind ridiculous amounts of debt, and be willing to be at the mercy of possible (but imo unlikely) changes to immigration law entirely disrupting your career.
Oh no I completely agree with you and did keep my grades up for the reasons you’ve cited. There is no guarantee of anything past articles and employers will ask for a transcript in the earlier years of practice. I don’t think people should stop caring once they land a 2L summer, and I honestly don’t think people do. Like sure, law students love to brag about how little they’re studying or how little they now care. But make no mistake, they still care lol
I would say it depends on the practice area and the city. Criminal law is probably most conducive for a sole proprietorship structure, but it would be very difficult to start in the current Toronto market without any real experience to stand on and clients with certificates that they can take to hundreds of lawyers. Personal injury is also difficult to start in any city because most cases are now taken on contingency fee, so you would need to be able to maintain your practice for several months without any income coming in.
The above examples are unfortunate because they engage access to justice issues. That being said, there are other areas where you could pick-up work. Everyone needs a will, and there are numerous self-represented litigants in family courts. Social assistance, landlord and tenant, and employment law.
You should ask yourself whether you're the type of person that should start a law firm. While it's great to have your name on the door and own it, you have to take care of more than just the legal work. Practising in association with other lawyers or in a multi-discipline practice is a good way to reduce your expenses, workload, unfamiliarity, and overall risk of failure.