Any Sony A7s owner knows there are a few things this camera needs to get the best possible quality out of it. If you want 4K footage, you simply can't record to internal media, so you'll be adapting a recorder like the Atomos Shogun. The battery life is also terrible, so a decent external power option might be the IndiProtools Power Pods (found here).
With these accessories, you'll need a solid way to mount it to the Sony A7s. There's a number of rigs i've shown in the past, and this is just another great option to consider for your A7s. The CAME-TV Sony A7s Cage is available in a variety of bundles if you need extra items such as a Mattebox, Shoulder Pad, Handles, etc.