As Brian H stated make a list of exactly what you wish to do!...
Well put. The more you can plan ahead the better off you'll be!
As I've learned new tricks and added new things, my system has become an "ongoing work of art". The down side of that is it would be a nightmare to recreate and takes me a while to pick available HC/UC/flags for anything new. I haven't even gotten a cable to play with the X10 floodlight cams I've had before AHP was around.
Regarding House Codes... I have a mild paranoia of HC "A".
I try use HC "M" for most of my macros with HC "D" for the telephone macros. I also have a HC set aside to for dedicated items that are only controlled by macro. I believe I have more macros than items for them to control.
Even if it takes 2 hours to figure out how to automate something that might take 5 minutes to do manually each time, it's rewarding to see things work automatically.