WA9ZZZ's answer missed the issue of control of the repeater. The repeater must be under control of one or more control operators, or under automatic control, at all times when the repeater is on. There are three types of control:
Primary control, where a control operator is physically near the equipment and monitoring the repeater, ready to intervene as ...
The regulations for an amateur radio repeater are fairly minimal. To answer your specific questions:
"Does one need a particular license?" Your license must permit transmissions on the repeater output frequency. That is, general or higher for 10m, technician or higher for higher frequency bands. There is no special repeater license. (There used to be.)
I am guessing that you programmed a receive tone requirement. Try programming only the transmit tone and leaving the receive tone not required.
I don't have Chirp available right now so I can't give you the names of these fields.
I don't know any radio firmware that would support blocking a specific ID.
It would be easy to implement in MMDMHost.
Call Alert is a ringer function. If a radio receives a call alert signal then it rings and sends back an answer to the caller and the caller radio shows a message about the successful delivery.
Digging into this further I found something that might be what I'm looking for, SvxLink.
While this might work I'm still curious about other options. Once I clean up some computer and network issues about the house I'll play with this.