A good landing page is one of the tools you’ll need to triage the other parts of your funnel, so it’s imperative that you get it right first.
You don’t have to be an expert to start. There’s a decent argument to be made that you can’t be an expert when you start, but that doesn’t mean you have to start at square zero. You can borrow expertise.
The page on your site that most directly impacts your profitability is the one where you ask people to join your mailing list. If it’s not good enough, your business will probably fail.