For (B), I'd say that there isn't much time to leave the airport. I've done it and gone into midtown for an hour or so on a three-hour layover, but that was coming off a red-eye and leaving on a 11 a.m. flight, so the terminal was pretty quiet. For a 7:40 p.m. flight, the terminal's going to be a lot busier due to the international push.

For (C), Delta uses Terminals 2 and 3. The terminals are connected by a walkway on the secure side, so if you choose to stay airside and arrive in one terminal and depart another, you won't have to reclear security.

For (D), I don't know if there are computers in the CRC, but there is T-mobile wireless, which is a fee. I don't know for sure, but the T4 SkyLounge (operates as a NW WorldClub, so a CRC member should be able to get access) might have free wi-fi...it's one stop down on the AirTrain.