Until LMMS I used onlinesequencer.net and to be honest, I liked its piano roll much better than that of LMMS, even though it was nothing but a piano roll. So I was thinking maybe you could add different looks to LMMS like "Simple" where the p r keys wouldn't look like actual keys but more just white and black buttons in a keyboard pattern. Another thing onlinesequencer had that I liked a lot was a key guide where you selected a key and it would darken the notes not part of the key. It really helped me follow the grid. If my explanation isn't good enough then just look at it and see what I mean.
But for key&scale
Scale tool:
In piano-roll select:
the scale you like to use, 2. right-most in the picture
to set the key in that scale:
Right-click that piano-key
Select mark current scale
Now lmms show you all notes that belongs to the scale in that key.
Perhaps you also can use this:
https://www.youtube.com/watch?v=ZEgx-_hMFYg