Owning your own home

Update I’ve dug out the trench at the front of the house (where damp is showing internally) to half way down the first course of bricks.
The red circle shows a load of brick and concrete (an old garden wall possibly?). It’s about 120mm or so above the level to which I have dug, shown in green.

1. Could this be contributing to the damp? If so do I need to try to remove it with a hammer and chisel?
   
2. Do I need to remove the parging? It’s not in good nick but I’m nervous about exposing the wall more and getting into a situation that rapidly gets out of hand. Can’t really afford a big bill at the moment.
   
3. My neighbour has recommended this Dryzone stuff. He’s planning to drill into his wall with a 12mm drill and inject it at various points. Is this likely to do any good in a solid wall?
   
   

Lots of questions but I’m out of my depth so open to more suggestions/advice. Thanks again to @TW for his thoughts a couple of days ago!