Heres a few helpful answers to your questions
If you are wanting the best quality image, then the Mk3 is for you. If you work with groups and sharing images on multiple devices is important, then consider the Mk1 The Mk1 can share with up to 4 devices at once.
Mk1 and Mk3 battery life should be up to 4 hours continuous use. Switch off the camera if not using for a period longer than 5-10 minutes, then reconnect wifi when ready.
Contact us and a solution to your specific needs can often be found. Sometimes not, but it’s worth a discussion.
That’s fine you don’t need to be connected to the internet to operate the camera.