I think you are getting way to caught up in measurements or specs. Rega doesn't publish specs for spacers needed with specific cartridges or cartridge height. Nor do cartridges publish these specs (at least any cartridge I have used). There is no spec for VTA. It is up to personal taste. Level is the starting point.
Just put in spacers to get it to somewhere near level. Then measure the height of the arm (or cart) with respect to the a record with a small one or two inch ruler (you can make your own). Fremer explains this in his DVD. You can use this as a starting point. Then, add or remove spacers as necessary according to your listening tastes keeping in mind your initial, measured reference to a level arm. With the Rega, this requires some bit of audio memory due to the task of replacing spacers is not immediate.
I think you should be more concerned with aligning your cartridge, getting your cartridge loading correct into your preamp, and VTF.
For most cartridges, you simply want it level or slightly up or down from there.
Finally, you don't need to figure out height and spacers needed before you order a cartridge. Get the cartridge and if you run out of spacers, use $2 washers from your hardware store. If those make you uncomfortable, then order more $30 spacers.
Btw, I have two tables, one of them is a Rega P5. I am using a 1mm brass washer with my Denon 103R. Many people like 2mm. There are no set rules to this.