@4 personally I'm using damage reduction over def, and given that I plan to use init and crit, I can't have both. I also have combo for when that is "needed" to make a ninja trigger with normal hits. Of the 5 listed, def is probably the least useful. There have been mixed test results according to different people on the effect of damage reduction vs def. Direct comparison usually find them similar, but that makes damage reduction better because it also applies to nin damage.PS: control actually works. I only have one because it's a red, but it's always amusing when you shrug off their CC..... they rage so hard.
@6 maxing nin/tai pen is a questionable choice. It does give you power, which is good for qualifying for TI(you need 32k for the awesome one), but it doesn't help you in battle(according to test people have ran). In theory, masuri is supposed to match based on power once you hit 85, we all know the match making is shaky at best, but still, I'd like to MINIMIZE my power while having the most fighting strength possible. So those two are questionable upgrades (by the same token, I'm not equipping my injury runes, luckily those you can equip for the power boost for TI qualification and then un-equip when not needed)
@11 Try always do difficult, and for both SA, 2 person team (of similar level) is easier than one. In Hidan SA, only one person need to carry CC to stop the OP skills while the other can focus on damage, which makes it go much faster. In Hanzo, 2 person have lower combo per person requirement for stage 2&3, which is the most difficult part for most people. (combo requirement is 1>3>2). So if you have trouble doing difficult, get a tag team, don't waste chance on lower difficulty unless you can't find a partner and can't solo no matter what.