I'm in the process of upgrading an old SeaTalk 1 network (ST60's) to combined SeaTalk 1 (old RL70C, ST60 Wind and ST60 Depth) and SeaTalk NG (new P70 and i70s). This was driven by replacing the old ST5000+ autopilot to ACU-200. You are correct that the i70s shows all the data, so you might think you only need one or two displays. I've decided that I want depth to be always visible, so not a candidate display for a page on the i70s. I could probably eliminate the ST60 wind, but it is one of the more important displays.
Although, not too complicated, your upgrade is going to take some careful planning. Plan on needing lots of the Raymarine SeaTalk NG backbone (blue) spur (white) cable(s), 5-way port or tee, the SeaTalk NG to SeaTalk 1 converter, two SeaTalk NG terminators, and possibly a NMEA
2000 to SeaTalk NG cable (if you have NMEA 2000).
Study the Raymaine SeaTalk NG diagram
-- everything is shown.
As mentioned, the ITC-5 will put all your transponders on the SeaTalk NG network --or-- you could find the older SeaTalk "Pods" for wind, speed and depth. I plan on replacing the speed pod with an ITC-5 when I have the time.
Last weekend we tested the autopilot and instruments. Very very nice -- I'm happy with the upgrade. However, on the i70s, there's so much information displayed -- I now want to simplify the page display (speed, AIS
, date/time, temperature -- I don't need wind, compass
,.....and all the fancy multifunction displays). You can add/remove pages, and customize the display -- there are 100's of page display options. I want to keep it simple.
Still working out a few issues with NMEA 2000 and SeaTalk 1 (via SeaTalk NG). Overall all the old SeaTalk 1 data bridges between the SeaTalk NG and NMEA 2000 networks -- it just works!