* Which port does ssh_to_job use to make a remote connection to the execution point where the job is running? Is it 9618 or the default ssh 22?
It's port 9618.
* Is there any extra configuration necessary to make sure ssh_to_job works beyond the default setup? Particularly if I limit traffic to just a few open ports.
If you allow inbound port 9618 on your execution points (that is, the EPs are _not_ using CCB), then no; HTCondor tunnels the traffic over its own connection.
In order for the various file transfer plugins to work, can I just have the relevant ports open on the access point or do I need to make sure the execution points also have firewalld rules configured for https, ftp, or what-have-you as well?
The file-transfer plug-ins should (generally) only ever want to make outbound connections, but they will be made from the EPs.
For an single htcondor pool, should one be able to directly ssh to the central manager or should it be only accessible through an AP?
Submitters should not (generally) need to ssh to the central manager.
-- ToddM