With not much free time available in a first place, I yet have to divide it between modeling as main hobby and other side projects. The projects are most of the time somewhat related to modeling though. Here is short list -
CNC shop setup - I spent quite a lot of time buying used and new parts, assembling machines, researching available stepper and servo systems and finally assembling my own CNC Mill with Xylotex drives. Process was lenghtly, expensive and took quite a lot of effort. If I had to do it again, I would rather buy complete CNC ready Sherline machines and ready to use Xylotex boxes. That would seem like more cost upfront, but would save money at the end, requires lot less effort and be much faster. Anyway, I eventually got machines up and running and now can produce parts on my Sherline CNC Mill and manual Lathe machines.
CNC software development - Apparently there is no CAD/CAM package among commercial systems priced to be affordable by modeling hobby enthusiast. Unless you produce stuff for sale and it makes very good profit, you wouldn't be able to afford invest few thausand dollars into commercial CAD/CAM system. So I set out to find free open source alternatives. I found CAE software called Salome, which includes pretty powerfull geometry module. It doesn't have suport for parametric modeling, as commercial systems have. But it's based on robust and powerfull OpenCascade platform and provides most of other typical features of 3D CAD. All my 3D CAD models created to date, were done in Salome. Situation with CAM is not as good. There basically isn't any feature complete free open source CAM system at the moment. Lot of different open source CAM projects were started and stalled or died over years. Two recent ones, which still alive and showed some promissing potential are PyCAM and HeeksCNC. HeeksCNC developers apparently found Adaptive Clearing code created by guys from freesteel.co.uk site and integrated it in. I've being testing and helping to develop features for both projects. PyCAM was most instrumental in creating toolpath I used so far.
Machining parts - apparently making parts on CNC and manual machines takes quite a bit of time and effort too. Beside stock, supplies and cutting tools aren't that cheap. Surprize. I did not realize how much I would need to invest into machine shop, before I can produce parts, which would otherwise be printed via available services on 3D printer. In theory in a long run machining my own parts should have being less expensive then having then 3D printed all the time. In reality I still have to send some part for 3D printing, because I could not machine them and costs of running CNC machines isn't low either.
Custom paint booth building - this is another project I initially took on to reduce costs, but ended up paying more in the end. Again it took a lot of effort, more money then one ready to use and quite a lot of time to finish. It's actually not yet 100% finished, but basically usable.
Long winding post. But at least some of the side projects are finished or almost finished and I can concentrate on modeling more. Oh no, wait, there are more projects on a horizon. Need to cast resin copies of F2002's seat, so have to master resin casting. Then will have to print some custom decals for R25 too. Never ending story, but keeps me busy and sane.