"Are later model hard drives compatible with this model?"に関する回答Any hard drive with a working SATA port can connect and work as a storage device in your time capsule provided it is standard size or smaller. Replacing the drive is extremely easy and step by step instructions can be found in a future repair guide.
"Can I replace one ethernet port?"に関する回答Unfortunately the entire set of ports has to be replaced as they are attached as a group to the logic board of the device. A future repair guide will show how to replace the logic board and with that your dud ports.