Just sent this via email...
The Raymarine specified dimensions are at this link:
http://www.raymarine.com/view/?id=3021 The outside diagonal is 15-3/4" (used a tape measure and had rounded edges so use as rough, not for cutting)
There are no issues at all with this display. I went to an All B&G system and replaced it with a Zeus 3. 12".
I kept my Navionics chart card, so you'd need to get charts for your area from Navionics, CMAP or the Raymarine Lighthouse charts.
Since you are interfacing to TackTick - the Cats meow is the Micro-Talk Gateway that couples the TackTick stuff to NMEA 2000. You'd setup a NMEA 2000 bus with the e125 and the Micro-Talk and share data between them.