Hiroya Oku likely starts with a concept or story idea. Then, he sketches out the characters and plotlines. After that, he refines the details and adds depth to the story through continuous revisions.
Well, without having read the 'takarakuji de 40 oku atattandakedo light novel', it's hard to say for certain. However, given the title, it seems likely that the story is centered around a situation where someone has come into possession of 40 oku, which could be a very large amount of money or some valuable asset in the context of the story. It might explore themes such as the impact of sudden wealth on one's life, relationships, and personal values. The 'takarakuji' part might imply that this wealth was obtained through a lottery - like event, and the light novel could then detail the various adventures, challenges, and emotions that follow this major change in the character's circumstances.
I think it depends on his inspiration and motivation. If he has a story he's passionate about, there's a chance. But it could also be that he wants to take a break or focus on other things for now.
I don't know. Making a new manga is a big decision and involves a lot of effort and commitment. We'll just have to wait and see if Koyoharu Gotouge decides to do it.