Brian,

1. You'd need one SS1L/S per circuit. The SSR is used only in 3-way or 4-way setups where more than one switch controls a single light.

2. That depends on what you want to do. I posted the detail page on the IR543 page last night ( [Link: members.home.net] ) which explains it's limitations. The IR543AH removes the one house code limitation but is otherwise identical.

Read my new IR543 page and let me know if it leaves any questions unanswered. The IR543AH page is probably a few days away. I'm waiting for a copy of the IR543AH's users manual so that I can ensure the information I post is accurate.