Frankly, with that level of skill you’re going to be really pushing it to get anything solid and “scalable” on EC2. There’s lots of moving parts to Discourse, and while you can tease them all out into their component parts to run on Amazon’s proprietary stack, it requires a fair amount of skill and experience to do so without causing everything to burn. It’s also not particularly cheap, when all is said and done.
The cheapest and easiest way to get a Discourse instance up and running is to just stick it on a DO droplet. Scale it up by upgrading to a bigger droplet as needed. By the time you’re on DO’s biggest droplet and still running out of steam, then you’re paying so much that one of our managed services is a good deal cheaper (and easier, since we take care of all the infrastructure management).