Are you a experienced with Shpify Plus, apps and adding coding ?

We have X3 shopify plus website's, we host and sell lost of sports clothing and also custom sports clothing for sporting teams. As we grow we need to add new features and functions to our website for online shopping, we need to add coding to our "Grid" theme or coding to our apps. We require a person to successfully made adjustments to our theme coding to add these features and functions for on line shopping, ordering, email marketing, & shipping.