More sets of questions for people with time

1. I'm cooking up some shield pulse builds, so keep a lookout for them. If you don't end up liking them, Saber can save you 20k feathers promoting someone to harvest the slaying edge. Alternatively, you can actually play him even with the atk bane - he tends to be extremely passive anyways, just making himself an indestructible stone wall, so the atk bane arguably plays into that, especially if he has +def.
2. Depends on your build and team. I'm using +spd -res with spd buffs; I wouldn't want to switch to -spd without giving her guard (not that I want to switch anyways).
3. Looks like you have plenty of refreshers, but if you're the type that uses lots and lots of them (some people have playstyles that involve 2 or even 1 glass cannon and a bunch of WoM dancers, see Omni H on YouTube for example) then 8-10 is perhaps not too many. By the way you're talking I don't sense that you feel a need for more. Besides, refreshers often do their job fine without being built. I use a level 12 regular Olivia in AA sometimes, and I used her flying alt without even leveling her the day after I pulled her, also in AA. But keep in mind that if you're taking a team into...chain challenge or something, sometimes they're good as colour checks (ex: both of the non-flying Azuras with base kit), so regular Azura can fill spots that her other two alts cannot.
4. If you go to inherit skill, there's a search-by-skill function. You can even see which units need to be promoted to be able to get the skill off of them (gray checkmark as opposed to blue).