Okay, well, for the first, it won't pose a problem UNLESS IRCC calls your employer to verify your employment and whoever they speak to reveals that you haven't actually been working under NOC 0114 for 7 years...
For the 3rd point, as long as the letter points to which entity you're actually employed to, it should be okay (even if it doesn't, you should be okay, but you always want to ensure all of your i's are dotted and all t's crossed). I also work for a larger Group (umbrella company) with multiple subsidiaries/entities but I'm actually employed to a subsidiary (as most of our employees are). My letter is on the Group's letterhead, but the letter has a clear sentence explaining which subsidiary I'm employed to.