Ohhh, so much stuff, so little time....
I've been mucking around with GIS (Geographical Information Systems - Google Maps is a basic GIS) and GPS (Global Positioning System) since the late 1980's. A more sophisticated GIS system has a database entry attached to each element on the screen. EG http://www.land.vic.gov.au
will get you into the planning schemes and overlays for each property in the state. Even this is fairly basic.
Questions you need to answer are
Who is this for?
What software do I have, and what does my audience (if any) need?
Am I duplicating existing effort?
How much data will I produce? How will I store it and back it up?
What data do I want to ultimately collect? Am I going to collect it all now, or stage it?
What data layers and symbology will I use? Is it consistent with similar maps?
How accurate is the data I plan to use, and can I accurately convert it from paper to digital? Incorrect or misleading info can be worse than nothing.
Be careful of copyright. It's unlikely as a hobbyist you'd get pinged, but acknowledge your sources.
Float your ideas here, and i'm sure you'll get some useful feedback.