I've only got one course so shouldn't it automatically go to course landing page?
With the new Site Builder feature, we have added in a Home Page so that your site will always have an initial start page. You can customize this page though to be specific to one course though (and as such, not design a seperate Course Landing Page)
If at the moment you only have 1 course is it advisable to build the Home page as your course landing page?
With only one course When I am sending link to customers would I send them the link to the homepage or course page?
The answer to this really depends on your future plans for your Business. If you're only ever going to have one course, it's definitely a good idea to just build the Site Landing page as your Course Landing page and distribute this link. But if you're going to be adding courses in the future, I think it makes a lot of sense to build a specific Course Landing page and distribute the link to that. You could even find a middle ground, but including CTA buttons on your Site Landing page to purchase or to find out more information. It's up to you! :)