Focusing on the back lever is a good idea…but since you can hold a tuck planche I think your shoulders should be strong enough for it already. Still, it’s a great full body strength conditioner and will help you to mentally understand how to physically approach the front lever and planche. Plus, it will take much less time to get down.
Besides that, I’d suggest continue focusing on press handstands, stand to stand bridges, and pistols. You could also work on the muscle up, but really the back lever is a fine substitute. Regardless you should be doing plenty of pull ups and straight bar dips, which forms the strength foundation for both of those moves.
For the stand to stand bridge, all I did was build up to a 1 minute regular bridge, then started doing one arm/opposite leg bridges for about 30 seconds each side (if the balance is an issue place a finger of the free hand on the ground or a wall, ideally the pinky). This was during the warm up for my daily workouts. Before long at all I was able to stand out of it, and once I did that I had the confidence to lean back into the bridge.