Newbie here. No network experience but already running 2 TOR instances: 1 TOR service + 1 bridge.

I would like to "upgrade" to TOR relays but have a few questions relating to hardware needs.

The [TOR-friendly] ISP I'm looking at have these 4 offers available:

[1]

1 core @ 3.1GHz

1 GB RAM

10 TB/mo @ 5 Gbps BW

[2]

1 core @ 3.1GHz

2 GB RAM

10 TB/mo @ 5 Gbps BW

[3]

2 core @ 3.1GHz

4 GB RAM

20 TB/mo @ 5 Gbps BW

[4]

3 core @ 3.1GHz

12 GB RAM

30 TB/mo @ 5 Gbps BW

From relay requirements, my understanding is that [1] is what is expected for a guard or middle relay and [2] for an exit relay.

My preferred choice at the moment is [3] where I would like to have 3 relays (one of each type; 3.5 GB RAM needed). Each relay would be limited to, say, 6.6 TB/mo BW. This would allow me to experiment and get used to the network and its requirements.

My questions is about future increase. If I want to increase my offer to the TOR network I could:

Negotiate with my ISP to increase my BW to 30 TB/mo while still running on [3] and increase each BW limit to 10 TB/mo;
Move my 3 relays on [4] and increase each BW limit to 10 TB/mo;
Move my 3 relays on [4], add 2 IP addresses and 6 relays (2 of each type; 10.5 GB RAM needed total), and limit each relay to 3.3 TB/mo.

I guess my fundamental question is what is the advantage of running multiple relays of the same type, on the same server? I see some operators running dozens of them, all in the same country, same ISP. Why not just a single relay running with a large capacity? Also, is there a requirement for the number of relays per core? (Maybe this is the answer to my question.) I know my bridge is currently keeping one core of my 2-core server constantly under load.

Thank in advance.