They will not restrict you from purchasing cloud app storage based on what you may decide to use the cloud storage for.
Some of those apps listed work fine on a 512MB/1CPU virtual box.
They care not what apps you decide to use on that low-end virtual box. They do not care if you buy the low end package and attempt to deploy Discourse onto it and use it for a medium to large community. Well, depends if they charge for overloading the CPU, but neither here or there in this discussion.
Same as DigitalOcean, really.