I remember there was something called BAD ELF. Check out at Amazon. You can read up at Panbo.
Back to your post though:
I think you would need a converter to convert the NMEA
out from your B/W plotter into the wifi
But 1st check out your plotter delivers NMEA
out via (I guess) serial
An example of one such converter is here iMux - The Brookhouse NMEA 0183 Wifi multiplexer
There are also other equivalent products from other manufacturers, fish
for the gadget that will serve you best.
For the charts
try the free US charts first. Many people like them. Make sure your iThing has software
to display the charts and your GPS
position against them.