Ok, first the copyright laws can differ from country to country so there is probably not an overall answer to that. What you describe has a complete analogy in the graphic/design market. The pre-production for print. Design agencies create files with copyrighted fonts and/or images. So it maybe is an idea to go to a printer (or design agency) next to you and ask there. They know exactly how they deal with it. I think it shouldn't be a problem as long as you can guarantee that you don't use the things you get for your own business. I see another problem in this business idea. The problem how these data come to you you want to render. When i look at my Vue files, they are normally so big that they can't be sent via email or ftp loadup. So they need to be sent by post. That means two days (to and back) minimum. And especially the clients you look for may not have this extra time. OR, you concentrate on the regional market around you. Then there is the question wether that is big enough. I used a service like that 3 times in my business life (so far). Long long ago of course. We are a German based company. #1. The render service was in Ireland. We lost the client because the courier was not in time (strike on an airport) AND, we then realized that there were bugs in the rendered video. #2 I had to fly to London finally to be able to set up everything correctly so that we are able to reach the deadline. Not much profit on this job because of the extra travel costs. #3 The rendering was so long - you never know exactly how long it will be beforehand - so that the costs exploded. Render times you pay per time frame.Not a profit, a loss was the result of this job.

One day your ship comes in - but you're at the airport.