I changed the filter the first time I changed some fluid, at about 80,000 on one atx and 200,000 on our other one. After that I have just drained fluid via drain hole in pan and replaced that amount.
No, I never bother with that, all of the complicated proceedures are just crap. I used to work for a Holden Stealership, admittedly on simpler autos but I did rebuilds for about 5 years. I am firmly of the belief that its just not that complicated.
100ml over or under... I cant say with any proof but I think no. I always err on the side of putting more back in than comes out so I think both of my aurions have above the correct fluid level. I have never done the proceedure to check. However, both function perfectly and my one gets flogged a bit, not my wifes though.