Just go to the corner and cross at the light towards the Paradise Pier hotel (you can see it from the road). If you start walking down the side opposite of Paradise Pier Hotel you won't have to cross the street again. Then just walk straight up the street (I think it is called Disney way). When you get to the entrance of the Grand Californian (at the stop light across from Paradise Pier Hotel), walk into the Grand Californian entrance (so take a right). Then once you are up at the hotel there looks to be kind of a breeze way and you can walk through that and then hang a left to get into the lobby and once you are in the lobby there are signs that will tell you which way to go. Or you can just walk directly into the main entrance/lobby.
When you exit the Grand Californian just pay attention to where you enter into Downtown Disney, as that will be where you go to retrace your route back to the Stovall's. There is currently Anna and Elsa's Boutique next to the entrance to Grand Californian.
It is really an easy walk as long as you cut through the Grand Californian. Chances are there will be people heading in the same direction in the morning. The walk itself took us about 15-18 to the esplanade.
My BIL/SIL stayed there last year. They said they crossed Katella and walked up Disneyland Dr to the GC and entered there then followed the signs to DTD and and then walked to the gates through DTD.
When you exit the Grand Californian just pay attention to where you enter into Downtown Disney, as that will be where you go to retrace your route back to the Stovall's. There is currently Anna and Elsa's Boutique next to the entrance to Grand Californian.
I know I hate that Sephora is right next to it too because I hate all those perfume smells so I always have to walk past super fast if they have the doors open. Super strong perfume/cologne smells trigger really bad headaches.