RAM is mostly independent from streaming capabilities. The recipient needs RAM to store the buffer but the host machine would do fine with 16 GB.
SSD for config and database, no exceptions. HDD is great for the media itself.
Other suggestions: a machine with an 8th gen or later CPU, non-F variant. Those CPUs have an integrated GPU that can transcode several streams simultaneously without the slightest struggle. To utilize this, you’ll need to buy a Plex Pass and enable hardware encoding.