yes been thinking of adding 1 more 100 AH battery. Blue Ridge MNTS hard to say weather here is pretty unpredictable at best.Sounds like a plenty powerful system except for more storage depending on cloud frequency (from these simpleton eyes; hoping more experienced members will view these posts). Do you know how many cloudy days you typically get in winter? What area are you located?
The dongle is required for that invertor to communicate with an Android or iPhone app. Hopefully you know someone with a compatible phone that can download the Victron app for analysis. It is easy and can be deleted after.