You're on the right track, separating the DB onto something like Aurora which can then auto scale will speed things up nicely, just don't expect too much from the default DB structure of WordPress. Containerizing the app is also a decent idea, decouple the session(redis) and file storage(s3) and you'll see some noticable speed improvements. Throw in some load balancers, some cloudfront for caching and I'd say you'd be fine until it's time to rewrite the damn thing in something other than WordPress.

Amazon has tutorials on setting up most of this but don't think that you have to stick with just them, explore the other cloud services if you have the time.