If you’re just starting 1GB RAM and 1 core is fine, but a 20GB harddrive is on the small side. You will often not be able to do the one-click upgrades as you’ll have to frequently log in via ssh to do a cleanup action before upgrading. Unless you know that you will definitely have a lot of traffic I’d recommend (as the Discourse guides do) Linode or Digital Ocean’s 5USD/month 1GB RAM, 1vCPU, 25GB SSD options.