@EstherSTL, I think you will be fine with 5 GB with what you plan to do if you have an easy top-up. Do note that
@Tincatinker says that you will want to download the base maps. This can be done either by downloading a region as you need it using available free wifi or else download all the ones you need at home. Each app is likely to have its own method. Check out how to do this before leaving.
Voice calls over data, such as with WhatsApp, will use about 1 MB per minute so about 16 hours of calls for 1 GB of data. Long calls home may be possible over wifi but that depends on a number of variables. Research this now. Another use of data would be backing up your photos to the cloud but you should do that over free wifi when available.
A battery bank is a good idea. Besides using when needed along the way once you arrive at your daily destination you can charge it and then use it at night to charge your phone. This helps prevent theft of the more expensive phone.