@2. I do it often but I use especially the fraction inch.
Usually I use the metric system but, some time, I've have metrics with many decimals when I try to be precise in measurements.
At this point I switch to fractional inch and I receive more simple dimensions like 4' or 3'1/2.
Why's that?
The production of construction supplies still use the imperial system for their products and they use simple numbers like 3'x5' or whatever.
Considering this, a plugin idea, is to have a local calculator or unit converter.