Games digital distribution platform

That's a big question - actually, many big questions. I'd suggest that re:Post isn't the place to ask that - mainly because it's a discussion rather than a "here's a single way to do this". Even a single way would (probably) take several pages of notes; and that would lead to lots more Q&A. And there's no single one "good" way of doing what you're proposing - depending on the skills you and your team have; the preferences in design and so on.

I'd encourage you to reach out to your local AWS Solutions Architect to talk about this in detail - that way it can be a proper discussion.