Ability to add pages to One-Page/Index Page template later on?

Hello!

I have a client who wants a one-pager for Phase I of his website, and a multi-page site for Phase II, which will be launched at a later date. 

The Phase I one-page website should have a sticky header and nav items that smooth-scroll down to the corresponding section below. I know the Pacific template is excellent for this with its stacked Index Page, but I am concerned that my client will not be able to 'build onto' the Pacific template once he's ready for Phase II (a multi-page site). 

Does anyone have any suggestions for how to make this transition as smooth as possible for my client?

Thanks SO much in advance for your advice! 🙃

-Carly

I would advise the Brine template instead. I wrote a blog post below on how to achieve a sticky header in Brine. 
 

https://thompsonweb.design/squarespace-website-tips/fixed-header-in-brine