Is it better to have one server that connects to Tor and connect all the hidden services to that one server, or one server connecting to Tor for each hidden service? The Tor connections will all be originating from one external IP address. For the purposes of this question you can assume that I have unlimited resources, so the costs of running multiple servers instead of one should not be considered.
"Better" is subjective. There seems to be nothing against running multiple onion services on the same Tor instance, as long as it is running as a client, not a relay. (See https://www.torproject.org/docs/tor-onion-service.html.en#three)
There is a performance impact when running multiple onion services on the same instance of Tor, but there is no limit to how many you can add. (See https://tor.stackexchange.com/a/1391/12240)
I think Tor connects to your server(s) / service(s), not the other way around.
But anyway, to your question, I can't see how this is a Tor question. Tor is only a network contraption to pass connections on to those servers. And at no point you're suggesting you'd run more than one Tor process. So it doesn't make any difference for Tor to be mapping its connections to one server or many.
To host your services, the same guidelines would apply as to whether to host them in one server or many, just as if Tor wasn't there. E.g., if you think that a service may bring down the server and your solution to that without Tor would be to run multiple servers (i.e., for isolation), the solution if Tor is present would be the same.