In my experience, the action screws on a Mauser simply tighten until they stop with a firm turn of the driver.
Really, a feel thing rather than an actual measurement of torque.
I don't ever recall any coming loose either but if you are worried, it wont hurt to put a little wax under the screw heads which helps to keep them tight but may be more psychological than functional.
I have heard of mixing fine walnut sawdust with modeling wax or accraglass to build up the wood under the screw heads if you are dealing with a stock which has been grossly over tightened or if you want your screw slots in time.

As far as the recoil lug, both mating surfaces, meaning the rear of the lug which contacts the wood and the front surface of the lug where it contacts the back surface of the action lug are important. There should be as little gap as possible at either contact to really distribute recoil throughout the stock.