Opinions on my Marisa build?

Looks pretty cool, I feel like I want to use her more myself but unfortunately I have +spd LnD Lucina, +atk Fir (my merge project), and now +atk Leif so it gets hard to find times to use her over some of these other characters I have,
I might consider Desperation because 42 is pretty good and with her high hp it would not be too hard for her to survive a round of combat and be in desperation range. You could also opt for speed refined wo dao to hit 45 speed.

I would go with Desperation over Renewal. She may be able to sustain one blow on offense with her high hp, but she'll likely be killed on enemy phase if she's in range. And then the next enemy she initiates on she'll die on the counterattack without desperation. Renewal only works if you have ways of stalling, which isn't even possible in every scenario.

Also, reciprocal aid could get her in desperation range at the start of the match without having to get hit first.

You can also pull for Ayra or Brave Lyn right now and give her swift sparrow over LnD and improve her bulk.

I'd suggest running Reprisal and Desperation actually. Your build looks good, but with Reprisal, after Marisa has taken 50 damage, she'll do 15 bonus dmg guaranteed, plus the 10 from Wo Dao. Switch out Atk+3 for a Heavy Blade seal (she'll need support to run that well though) and you'll be a force to be reckoned with.

I think Furry would be better for her a slot, LnD is good but she don't need to be glass canon without defencess in my point of view.

Since we have so many speedy red unit builds, I opted to give my Marissa an enemy phase build that's also quite budget. I gave her def refined Wo Dao, Bonfire, Earth Boost, and Renewal with QR seal. Otherwise she can have QR in B slot but Renewal is nice to have as sustain. With this, she can hit 40 def in both phases. If Bonfire activates, it allows her to hit incredibly hard.