Canvas size product size point size consistency

I am generally happy with the software but am having to remove/reduce the features which are not working.

Eg there seems to be several places to change sizeing

The canvas size, the product size in pixels , the product size in mm, and a couple of other places like the UI size… none of these are eplained clearly and it takes a lot of experimentation to get a canvas size that fits inside the ui size and that outputs a correct resolution. All I want is an a4 sheet size. 

I kind of have up and just made all the sizes the same 1000 x 700 pixels which works fine for viewing but is wrong for output resolution. 

Also the text point size is wrong compared to Inkscape or word point sizes. What is the text point size based on? And how do I get it to be correct in an a4 sheet?

Like I say I am generally happy but think more documentation is needed to get up and running.