Can you help me with this simple question?

I am ready to install PeerTube on a new DigitalOcean VPS Basic Droplet.

After reading as much as I could, I am going with the $15.00 a month:

2GB (memory)
2vCPUs
3TB (transfer)
60GB (SSD disk)

Here is my question: Should I create another Basic Droplet ($5 monthly) to transcode the uploads separately?

You cannot transcode uploads on a different machine (for now at least), so no.

Thank you for this.

One more question: DigitalOcean has a scalable object storage solution called Spaces. Does PeerTube offer some way to take advantage of this? Here is their promo page about it:

Yes, since it claims to be s3-compatible, please refer to https://docs.joinpeertube.org/#/admin-remote-storage

Awesome. Thank you for this!