A big factor for speed is how good or bad your ISPs peering is. Basically the bandwidth authorities will try and measure your throughput individually and based on their consensus your “observed” bandwidth is calculated and used to push that amount of traffic to your node. If you have a new node, it can take time for things to average out and get a real feel for what your node bandwidth is.
You can see what the bandwidth authorities think about your speed:
https://consensus-health.torproject.org/
Scroll to the bottom and enter your relay fingerprint/nickname and click Load.
Or you can search for your node here:
https://consensus-health.torproject.org/consensus-health.html
Yes, people can and do run multiple relays on the same server to maximize their overall bandwidth usage. If your hardware is beefy enough, go for it. Currently you can run up to 8 relays on the same IP - though that may change again in the future.
https://forum.torproject.org/t/tor-relays-8-relays-pers-ip-address-are-allowed-from-now-end-of-june-2023-on/8192
From what I’ve seen, it’s generally not recommended to run more than one type of TOR node on the same machine for security, privacy and overall tor health reasons. Running several middle/exit relays on the same machine seems to be the generally accepted method to more fully utilize your available resources.