I don't know if my plan is going to work correctly
If the experience of others is any indication, the answer is nope. In this post dated May 20, 2013, a developer documented his experience with Heroku versus AWS: "Why I left Heroku, and notes on my new AWS setup" http://www.holovaty.com/writing/aws-notes/
I would suggest using an Amazon EC2 reserved instance. To get started, you can buy a second-hand reserved instance reservation ("Third Party"). I recently bought three reservations for $20 down plus subscription of under $15 per month for the remainder of the tenancy (two years) to run them in three regions, and I couldn't be any happier.
Amazon can write faster to S3 than anyone else, so if this is an issue, EC2 has an advantage right there. Plus, Amazon will not make upgrades for you that would break compatibility the way Heroku has been known to. I hope this helps.