I need help with frame-by-frame animation

My first question is, is there any way to move multiple keyframes at once? Like I have each of the frames of my animation set as separate keyframes but they're in the wrong position on my screen, how can I select all those frames and move them together?

My second question is, how do I add things to the beginning of my animation without messing up all the timing? I haven't added the intro to my animation yet and have realised that when I try to move my animation along the timeline everything gets out of sync and it's just really tedious and annoying.

My final question is, is there any way to import a video with a transparent background without having to convert it to a gif? Because when you import a gif it imports the individual frames and then we have the same problem as the first question.