Merry Christmas B!
I always thickness my top wood to .140 prior to testing so as to level the playing field on material thickness.
Other than what you already covered, specific and constant spacing between supports, specific weight, etc. that's it.
Now the difficult part is building the database so that what your results are is meaningful. Or, in other words data from several tops won't mean much but data from say 50 tops becomes more useful.
Lots of us have done deflection testing differently and there is no right or wrong here just follow the scientific method, be consistent in your set-up, weights, etc. and understand in advance that you are setting out on an effort that will take some time and many tops before it's meaningful.
Lastly and something that was very important to me. When I started building my life was full of specific metrics for this and that and the other thing. I always wanted to be the sort of Luthier, the romantic version who can flex a top and know from experience at least to some degree what to expect. With this said be sure to take the time to smell the roses and do some subjective flexing too along the way.
One of our friends here and a highly contributing member in the past, Mario P. once talked about carrying around a small block of wood in his pocket to over time understand the feel of the wood. No jokes please...
. But I did this too and still have the two blocks of spruce and BRW that I carried around in my pocket for about three years. Every day these little sugar cubes of wood went with me. The TSA didn't appreciate it either but this is what I did. Don't know it it helped at all but I suspect that there was a calming influence not unlike worry beads....
