Should I build a full website or just a landing page for my agency?

A landing page is fine and is easier. Put everything a visitor needs to know to buy your service on it: the outcome first at the top, then how you deliver it (for example database reactivation, social media marketing and an AI receptionist).

A landing page offers one thing and drives visitors to one action, such as booking a call. Extra links to a blog, a contact page or a results page, or several different call to action buttons, pull visitors in different directions. A one page website can be treated like a landing page.

The smaller the price point, the less selling the page has to do. A low priced offer can be a short page: the promise, a guarantee, a few examples and a get started button. Extra services can be sold as add-ons later.

Even if you never present your site, have an online presence: prospects will look you up and judge you by how the site looks, and you will need a landing page or funnel once you advertise.