After reading many articles and reviews on the topic of internet on boats, I am seeking advice on how to upgrade my systems.   I find it difficult to understand the overall system and equipment requirements, and need some help to understand exactly what I need, and specifically what are the better options available today.   The boat is a 58 foot powerboat.   Here is what i have.   

2007 vintage Syrens wifi system that does not do anything anymore.  The website that used to show the list of available wifi no longer works.    There are a couple of old "cell amps" that I don't know what they do.  There are external antennaes for this equipment   What I want is:   wifi network on the boat that users on the boat can connect to and which in turn will be connected to internet when available.     I am leaning towards using cellular for external internet access rather than using marina wifi as those are normally not very good if they work at all.    Or I would consider installing both options.   Ideally two SIMs would be installed to allow me to have access to a couple of mobile operators.   I run Furuno TZT2 on the boat which has wifi capability but I assume I would simply connect that to the boat wifi after I set this up.   Currently the boat is docked at my house and can access my house wifi when we are at home base.  My question is what are the suggested equipment options to execute this plan, and how is it all put together?   Ideally what I install should be future proof to the extent possible.

Mainly the system should provide internet access for general use such as email, browsing, streaming tv.    I don't work from the boat so my needs are more convenience than absolute need.

Thanks in advance for the input.

Don