Zephiles' tutorial helped a little bit, but not to the extent that I need. How do you time 4 frames so you know when to move?

You kind of just need to get a feel for the timing. A slightly easier way to learn the timing might be to perform flurrie orientation lock glitches with X+A presses. If you press X four frames before you press A, Mario's facing direction gets locked. This can help you determine how long four frames is and all you'll need to do is apply it to goombella buffer.

If it helps, four frames is 1/15th of a second.

Can I get a link to the walkthrough? I cant figure it out either. I plan on doing my first stream ever this Thursday, and lately ive ben skipping that part (I know what to do, I just have trouble with the execution.)