Thank you for posting your question to the Ask Me Help Desk.
Recall the information that I posted for you on the roundoff already...
Link to roundoff info
Connecting your toe touch jump means being able to rebound out of the roundoff with the chest up.
For back walkovers, a couple thoughts...
A spotter is ideal but you could find a clear place to bridge up with the butt against the wall. Walk up the wall and kick over. Make sure that you keep strong arms because if you bend the elbows you will most likely crash. Adjust yourself further away from the wall as you get better. Eventually you can kick over from the floor.
To work your way down, stand with your back to the wall and arch back and put your hands on the wall. Then you can walk the hands down to the floor and back up again. Keep in mind that the feet will have to move too as you go up and down.
Ultimately, understand that this is a shoulder flexibility skill and not a back flexibility skill.
Constantly work the bridge so that you can push the chest out over the shoulders and have the shouders above the wrists or even further. Think of doing a bridge with your head by the wall and use the feet to push so that you can press the chest against the wall. The arms need to be straight. You should form a relatively straight line from the hips to the feet when done well. Sort of like a slide. This will help build up some shoulder strength and flexibility.
Good Luck!