It's quite a change going from a 60+ hour work week interacting with hundreds of customers to sequestering yourself in a shop trying to figure out what to do next. Most of us go through that stage once the honey dew list is completed or at least under control.
Have you considered any "large" projects that could span over months or even years? One of my first big projects was to build a small articulated end loader from scratch. I didn't really know where to start so I purchased a set of plans from CAD Trac. When I got them, I didn't like what I saw so I started redrawing them. The project spanned over 4 years with the first 6 months at the drawing table. I ended up with a machine slightly larger than the original and weighing nearly 3 times as much.
It was sort of a fill in project that took up any spare time I was willing to devote to it. According to the company the assembly project (if you bought their precut kit) was supposed to take about 40 hours. They no longer sell kits in that they were getting too expensive for most hobbyists. The last complete kit I saw advertised about 4 years ago had a price tag of over $11,000.00. I spent less than half that amount sourcing my own materials. All the materials and components I purchased for my machine were new.
I spent probably 500 hours redrawing components, another 500 hours sourcing materials and components, and another 1,000 hours or so cutting, machining, welding, assembling, wiring, and testing the machine before I ever lifted a scoop of dirt with it. It could have taken another 200 hours if I painted it as originally planned. Unfortunately, I ran out of patience, so the machine never got a proper paint job. It still works fine but isn't as pretty as it could be.
Over the years I've built a few accessories to make the machine more useful. I've added a snowplow, set of forks, and a log splitter. You can build just about any accessory you can think of.
Here's a link to the original CadTrac on their website:
After numerous requests CADplans has developed CADTrac, the articulated, 4 wheel drive, multipurpose tractor you can build using a welder, bandsaw, drill press, torch, common hand tools and commonly available parts. The all-hydraulic drive of CADTrac eliminates the belts, chains, transmissions...
cadplans.com
Here are a few pictures of the machine I built: