It is certainly worth trialling an instance. I could find very little information about server sizing specifics, other than, more videos, more disk, more users, more bandwidth.
They don't share how much you need as it is so varied on how many active users you have, how many connections to other server instances you have and what is being done on your instance.
From my experience.
500-1000 users (not online at the same time), you are looking at 2 CPU cores and 4-6GB RAM (Redis likes RAM).
Offload all media onto S3 compatible CDNs. Do not host it yourself! Not worth the disk space or HTTPS requests hitting your server.
If users upload a lot of video content, more CPU is needed as it uses FFMPEG to transcode video to whatever resolution and bitrate the host sets (you can offload this to GPU if you have one).
When I had an instance, it was around 1000-2000 concurrent users online during peak hours.
2x 4 CPU frontend servers for Nginx/Ruby and FFMPEG (these were load balanced via hardware)
2x 4 CPU backend for Sidekick (this processes tasks like new messages, pushing and pulling messages/content etc)
1x 4 CPU backend for Postgresql/Redis databases.
1x 2 CPU frontend CDN server that cached 250GB of media content in front of an S3 bucket.
When doing S3 on a budget, you want to cache as much as possible as requests cost money and so does bandwidth. This server alone was doing 250-500mbps on average 24/7.