Sorry, I'm not sure. I had the strongest sword in the game before that point (the bat sword or something; purchasable in the weapon shop) so maybe you need that one.

Edit: yes, you need the bat sword, the creator confirmed it

After you finish the new update main story completely, Horace will tell you to bring him cookies, go to Feasterra during the day, and inside his house in the second section of Feasterra, click on the dog house (it looks like a little hut with a dog bowl next to it. 

NOTE: You also have to have finished Horace's affinity completely. Can't access this part otherwise.

Yes, He appears randomly on Solitude Mountain.

Do you have the key?

Inside Grant's bedroom, click on the telescopes on the wall.

For the Cursed one yes but you can access it again with Dicktionary at the Library after. You can find him randomly in Solitude Peaks for the Dicktionary entry for the regular Dodoro.

not sure if this thread is dead or not, but no you don't encounter even the cursed dodoro only once—it's just that you can just only visit the '???' location at night. i would get any necessary grinding done during the day, or just take naps until nighttime, and then head out to the cursed dodoro location. stock up on three or four 'orc's favorite dishes'.

Inside the room on the wall, not on the balcony.

Did you do this first? The ones inside won't give you anything if you don't use the extractor out here first.