Who to promote!

In my opinion, fun comes first. I'd recommend Marisa since she's one of your favorite characters.

If Marisa is your favourite do her first. Depending on the status of your Elise, Pain+ fodder would possibly be next, or Soren.

If Marisa's one of your favourite characters then deffo promote her first, after Marisa normally what I do is that I'll promote units that have perfect IVs or are tempest trial/grand hero battle and promote my favourite 4* characters to 5* so I use them as merge fodder for the perfect IV 5*. Right now I'm just saving up on feathers so that when I summon the perfect Adult Tiki, Olivia or Felicia i'll be able to promote all the other versions of them and merge them with her.

Marisa. Not only is she one of your fave characters but she one of the better units on here. I've been meaning to build mine but damn have I been slacking

I built my Marisa (mostly) and she's pretty solid as an all-purpose red. Wo Dao+(Spd), Reciprocal Aid, Noontime, Fire Boost 2 (4* LA Eliwood), Renewal 3, Panic Ploy 2 (4* Valter). Now I'm just waiting for a Luke so I can upgrade the Fire Boost and Panic Ploy (and the option of Brave Sword+).

Of the others which I promoted, I only have a Soren, who is still outperformed by Nino. What I wouldn't recommend out of the above are Oliver (Doesn't gain important skills from 5*) or Henry (You can leave him at 4*+9 Raourraven-normal until you can afford to promote an extra to give him Raourraven+, since his attack is a mostly irrelevant stat).