Waiver - at the present time I happen to work for an org that sells Cyber liability insurance. In my previous work I did a lot similar items to what you talk about so I am describing what I used to do to help secure things.

1. as an individual there isn't a lot you can do to protect yourself from being hacked. Follow all of the typcial do's and don't (encrypt the wireless, don't broadcast if you can avoid it, use wired over wireless, find good router with good raintg on their security and change away from the factory settings), but otherwise not a huge amount. You could choose to log everything, but again unless you invest a LOT in expensive routers, you won't have any IDS worth bothering with.

2. if you have a wireless network for the house - consider having ANOTHER wired only router to connect your work machine to the rest of the assets. The modem itself usually provides NO security, so no I would definitely not just wire my PC into it (not even my home machine.

3. physical security tends to provide the easiest gains. I quickly got to a point where I never stored customer content on my hard drives. These days with USB drives being cheap and with ample storage, set up a separate USB drive for each customer, and plug it in only when you need to work on it. Encrypt any customer data at rest whether you think it's important or not. I also used removable drives for any temp files needed. If you have a separate "work" machine - use wired only, and if you can manage it - unplug it when you're done. Lock them up somewhere safe.

4. work out with the customer what the most secure way might be to send data back and forth. Unencrypted e-mail is just an invitation for a loss, and shouldn't be accepted period. Find whatever works for both of you and then stick to it (put it in writing as well).