Hi again
I wouldn't worry about registering the domain as a business at the moment. I would start off as a sole trader and if things go well then move onto setting up a limited company. That's what I'm doing.
I've also used Bluehost and they seem to be fine for WordPress based websites. It's a very good question about whether having a US based webhost can affect how a UK based business ranks on Google and things. Personally I don't think it does.
As for the other addons with Bluehost here are my views:
SiteLock Domain Security - I wouldn't bother with this one.
Site Backup Pro - I wouldn't bother with this one wither. Personally I do a manual backup of my websites.
Search Engine Jumpstart - A personal choice but again not one I'd go for.
Domain Whois Privacy - I do use this one, otherwise people will be able to look up your name and address.
However, these are personal choices so take the time to read a bit more about them on the bluehost website.
I'm not aware of the "make your website look great on a mobile" addon. I couldn't find it on the bluehost website. I don't think you need it because you will actually want to find a WordPress theme that is mobile friendly.
Again I'm not familiar with 1Page registration - perhaps you can send a link.
Hope this helps.