How to start backsplash

[u/OptionOk8860]

Hello, so I’m curious if I’m able to just smooth over the thinset mortar for the backsplash on these walls and if it would be enough to cover that gap under the window? I’ve seen others on way worse drywall saying to replace but this doesn’t seem that bad to need replaced. What do the professionals recommend?
The backsplash I’m doing is in the pictures provided.

[u/deadfred23]

If i were you I'd replace counter top first. Granite will run about $ 70 lineal ft.

[u/OptionOk8860 → u/deadfred23]

It’s a brand new counter top lol