From what I've read the pathfinder doesn't support AIS as you suspect. To set expectations if you were wondering, I'm not aware of a mechanism to display your radar
data on a tablet but getting your instrument and AIS data displayed is easily do-able.
As barnakiel says, your instrument data needs to be converted from seatalk
to NMEA-0183 for any phone/tablet app to be able to use them. Your RL70C should be able to do that but then you have to have it switched on all the time. You can buy boxes to convert seatalk
to NMEA-0183 such as the one barnakiel references
(now discontinued by Raymarine
, available second hand. Digital Yacht and others make equivalents). A neater option though is to chose a multiplexer which takes a seatalk input and does the conversion itself. The Yacht Devices one which barnakiel links to is one option but there are plenty of others including the shipmodul miniplex:
ShipModul Marine Electronics
Do draw yourself a diagram similar to the one in your original post but for your own equipment
out the minimum number of inputs and outputs you need to whittle down your product choices. You probably want seatalk input, an input for GPS
if that's not from seatalk (the lowrance plotter?), a 38400 baud-capable input for AIS and heading from the pilot. You probably want to be able to output (at least) to the pilot, the plotter and your radio
(GPS for DSC), all in addition to wifi.
For displaying those data on a tablet take a look at the paid-for version of openCPN
if using android. Navionics
is also popular for iOS and android and can display AIS these days but there are many other choices.
wifi multiplexers strike me as vastly overpriced. In the UK where I am they're north of £300. Various DIY
alternatives using such things as a raspberry pi also exist but they tend to be less neat and physically robust as the commercial
products so are not for everyone.