It's good that you're thinking about this, but you may be worrying a little too much. I find it hard to have a site about soap or homemade soap without saying soap, at least a couple of times. It's generally a good thing to have the keyword target in the meta description, Title, slug and a possible variant for the h1. So long as the content actually pertains to soap - you should be okay.
What I would avoid is writing:
"So I heard you like soap. Soap is my favorite thing. I'm so glad you like soap too. Let's have a soap party. Soap is amazeballs! You likely need soap in Poughkeepsie. Soapy soap soap."
A site has a theme. It sounds like you're going to keep that theme. You're writing will likely be Top 10 Decorative Soap Ideas for 2014, or An Amazing Tour of 'Soap Factory Here' in Paris.
My overall recommendation is don't be too pious. Your site has a theme, stick with the theme.
Yes, All in One can help you change your titles. If you're worried about repeating a keyword in your blog title, go to the general settings in your WP Admin panel and remove the site Title and the Tagline. Go to the general settings in All in One and scroll to title settings. From there, remove | %blog_title% from both Page Title and Post Title format then save your updates.
Enter what you would like in your title tags on both pages and posts. I personally see nothing wrong with 'branding' at the end of your Title tags, but you can now add your branding wherever you want - rather than having it added by default. But it's your thing - your site - this should enable you to do what you feel is right.