Uuh, I'm here at Richards and a prompt to talk isn't showing up. I've even at his house and see him??. .
Richard Hayward is another guy, he is living in Kilknoloch, he is not the owner of the watermill. You are looking for Thomas Miller, living in Donensbourgh. If you already talked with Thomas, ask him about where to find wheat seeds. Keep in mind that dialogs and story is progressing according to the player knowledge, so you cannot ask a NPC about a bucket if you don't know you need a bucket (makes sense), so to "unlock" sentences on NPCs you need to ask about them to another NPCs, just be sure to ask and read the whole conversation from any NPC you find, you don't need to run from here to there without any sense, as I said, you will not have the option to talk about something that you don't know yet, so just running randomly in the map finding NPCs will not help.
If you need more help, you can keep writing here of just join discord channel for faster response.