think F Takumi is decent enough to +2? Or use as speed smoke fodder

Speed smoke fodder unless you don't have any other good infantry archers.
S!Gaius is on this legendary banner, he runs a decent Brave Bow.

He's a decent archer if you're looking at him and just him.

Fallen Takumi 5* +1 has 1 more speed and 1 more HP while a +2 has 1 more defense and 1 more attack. So if you feel that it's worth it, then go ahead.

I'll probably keep one and use the other two for speed smoke fodder since a Fallen Takumi merge project probably won't be complete since only 3 has been issued.

If you need an archer, he is usable. He’s not top tier, but he has niche roles that he can fit quite well.

I may build mine for the purpose of bow/tomebreaking in AA. He has a solid spread, so I think it would be fun. I fought a fallen Takumi in arena, and while he whittled my health away on turn 3, I was still able to slaughter him without breaking a sweat.

I like the uniqueness of Skadi, so I'll definitely play around with him for the fun factor. But I won't bother merging. The +1 to the other stats is ok, but not worth it compared to being able to fodder off the speed smoke, in my opinion.

Also, there are enough other better archers, that even in things like Assaults, it's hard to see him being used competitively very much.

A full team of Skadis and a dancer. I have a feeling a team like that will definitely have cheese potential on GHBs.