In my opinion there's no such thing as a low maintenance stock site. If you want to host video, you would need a good script (not cheap) and a powerful VPS with huge amounts of bandwidth, or better host the files in a cloud storage like AWS, which could be very costly. It is also a very competitive niche so you would need to pull out the big guns in order to get your site on the first page of the SERPS. I would suggest to start with keyword research and a rough estimate of your initial investment and monthly costs like VPS, the cloud storage, mail server, etc.
I don't have experience with cpm ads, but you can do the math and if you consider it is worth your time and overall investment, then go for it. Good luck!