3. As far as I know, the dealer doesnt do mudflap installs, nor do you need them too. Super easy install. Check out Rallyarmor Urethanes, or DRT's. Theres also some great DIY options(Great meaning you put the effort into making it look good, not just slapping cutting boards on there).
4. Im on the dunlop DWS, and cant complain. However to me, tires are 100% preference once you pass the performance threshold.
5 & 7 : Subaru paint really is not the best. In any detail work for subarus(washing, waxing, ANYTHING) just take EVERY caution. ONLY use clean, noninfested microfiber/brushes, and only the best stuff. Honestly this should be the case with any car youve spent good money on, but regardless. I use mostly meguirs.