3000 developers doing what? Are they all online at once? Are they each creating 100 posts per day and view 1000 posts each or do they visit every other day and read 5 posts? Are you using CDN? S3 for uploads? The reason that your question isn’t answered anywhere is that it’s to hard to ask your question in a way that it has an answer.
There are guidelines for those settings depending on how much ram you have that get set automatically by Discourse setup. It’s the same for two containers as for one.
Mostly, you start with 2gb or whatever you think you can afford and increase it if you see that you have a problem.