1.Uverse is a marketing term and is completely meaningless when applied to actual service delivery to your home (which can take a variety of forms). Some "single" uverse installations are delivered over two pairs of copper wire. While it is certainly possible that the current phone wiring from your apartment to the MPOE of your complex is a single pair cable, it is far more likely that it is a 2 (or even 4) pair cable.
In order for you to get bonded Fusion service you need 2 pairs from your apartment all the way to the telco CO.
2. Self install is fine if the pair or pairs are already arriving in your unit. Most apartment complexes will not allow tenants to access the MPOE and therefore professional install is most likely required.
3A. Yes, you can use a router behind the modem.
3B. Or you can use the "modem" (which is actually a broadband router) to be your firewall. For bonded Fusion the CPE would be a Comtrend Nexuslink 5631 or a ZyXel P-663HN-51.
4. Definitely yes. Be sure to sign up for at least one static IP address (I believe those are free now) if you want to run a server.
5. If this is a residential Comcast package then running your own server is at least a violation of the ToS and some ports may actually be blocked. Sonic does allow you to run your own servers, so this alone might be a worthwhile reason to go with Sonic. If download speed is your primary concern the Comcast offerings are hard to beat.--
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