Hi Michael,
Question: Should you be selling services you don't know how to deliver?
Follow-up question: What if someone (unintentionally) gave you bad advice here and you acted on it?
Typically a business hires another business to provide a service they are experienced in delivering. I realise the only way to get experience is to do, but perhaps you should be learning on your own sites before moving on to clients.
To touch on your questions, local directories may be a very small part of a link building strategy, but they're definitely not the only part. Also, you are going to be extremely limited in the types of links you'll be able to achieve building to a 'coming soon' landing page. It also means you can't build deep links.
I would recommend reading, 'Starting A Link Building Campaign' here for starters: http://www.seomoz.org/beginners-guide-to-seo/growing-popularity-and-links
If, after reading that you don't know if you can deliver a quality link building campaign, perhaps look at outsourcing the job to another SEO until you're up-to-speed yourself.
I don't mean to be come across as an ass, I'm honestly concerned for both you and your client. I hope this helps.