That makes good sense. For conversion factors, multiply any dimension in millimeters by 25.4. In centimeters, you can multiply by 10 and then convert. For decimeters, by 100 then convert. The result will be in inches. Run out 3 or 4 decimals and round it as fits. Some places it matters, some it doesn't. That's essentially what I do with my models.
As an aside, I picked up a metric micrometer on eBay a while back for 3 or 4 bux. They paid shipping... It took 3 weeks plus to get here and I'm not sure how accurate it is. But I was getting it as a standby tool anyway. If I measure a 12mm shaft at 12.02mm, that's close enough for what I do.