You may also want to change the Direction on your Keyboard watcher to "Up" to prevent multiple triggers (since holding down the spacebar too long with the Keyboard Watcher set to "Down" can trigger the Keyboard watcher in the Scene your transitioning from AND the Scene you're transitioning into).
Adding a Multiblocker actor between the Keyboard Watcher and the Jump Actor is another way to prevent accidental activation of more than one Jump actor.
i don't have isadora now with me to give it a try but maybe try to put the activate scene actor inside the scene you want to activate. So when you press the letter for the scene you want live, it will stay activated.
For triggering videos with the arrow button you have to use the "keyboard watcher" actor. Assign the arrow key to the right to add 1 to the float counter and the arrow key to the left to subtract 1 to the float counter. This way you can cycle through your videos. To assign the arrow keys to the "keyboard watcher" actor click into the black field of the "key range" input. Type a single quotation mark (') on the keyboard, then click on the right arrow and again a single quotation mark ('). Do the same on a second Keyboard watcher for the left arrow. You will see an empty space between the quotation marks, but thats fine.