Running multiple accounts effectively is full time work 😂 I’m happy just using nostr. For your book if the goal is just sales/awareness, you could just pay for a targeted ad campaign to run on FB/IG between now and when it comes out. Set it and forget it and they’ll run it within your targeted demographics for you over the duration you set for the campaign.
My book is more of a ministry than a money making endeavor. I want the reach, but I also don't want to spend too much and lose too much. I'll think on that. My husband still has an active facebook account because of our business (rarely used personally). He does business advertisements, so he could do a book advertisement for me.