Shopify Developer

I am looking for a Shopify development partner that can do the front-end development for my clients.
To start off I have a specific task:

1. Client uses Shopify Brooklyn theme. The second, third and other product page photo's are displayed in full size. Client wants to have the second, third + product page photo's to have it as thumbnails, when click thumbnail it displays it in full size.

2. Collection page show by standard the first product image. Client wants to show a unique image on collection page, that are only displayed on collection pages, not on product page.

Please clarify how you would develop functionality 1 and 2 + how the client can manage the functionalities?