If using mapping for AtoB car navigation/walking round a city, is an Internet signal required?
If so how much roughly MB’s are used? I don’t want to go over my allowance (1GB)

Assuming you’re using Google maps and navigation, then an internet connection would be required, however you can download the maps over wifi before you leave. To do this, move the map and zoom out over area you need, tap the search box, and scroll down to the “make this map available offline”

Not directly answering but go to settings>data usage and set a monthly limit and view your usage by app/service

If you use an app with fully downloaded maps there is no need for a data connection. For guided turn-by-turn navigation on my Android phone I use Navfree

https://play.google.com/store/apps/details?id=com.navfree.android.OSM.ALL&hl=en_GB