A locknut should never have a washer between itself and that which it is locked to, so no washer between the nut and prop, or the nut and coupler at the inboard end. A thrust washer is needed between the outer end of the propshaft tube and the prop locknut.
To stop the prop walking the shaft out of the tube in reverse, something is needed at the inboard end. If the coupler and its locknut and a thrust washer allow this, great. If not, it is OK to stack washers to pack out the distance, you can use a length of tube, in some cases a collar fixed with a grub screw does the job. Whichever, there should be barely perceptible end play. With bearings and shaft in good condition, there should be no side play, either.