Question about multiple juggles

i finally feel confident in my multiple jugs (after a couple years or so of being able to juggle) and i'm mostly focusing on the tama. but that is because i have been able to get the rhythm down for the ken, so i mostly just need to worry about where the tama hole is so i can spike it.

i would say to focus on just the rhythm of switching between the ken and tama. thats kind of what i did as i was learning em

 

Long. I learned multiple juggles on 3 and switched to 4 and really honed them in, but it took a year or so.
All of the "new gen" kids learn multiple juggles on strings you can fit your whole hand into, so for learning, I would say go 5+ finger length if you want to learn fast. Whatever length will let you freely practice the motions of juggling without the string being an issue pretty much

 

Spinner is the first thing that comes to mind. You can even try a spinner and a bead, it works for some people (Ben Herald uses this method for example).
Another tip would be to watch how you release the ken. If you toss the ken up in any direction other than straight up (like even to the side a little), the string will catch onto it and begin to tangle. I've been noticing that I do this lately so I've been really trying to correct it. Ex: I toss my ken straight up during the juggle, but it rotates ever so slightly during the motion to where it comes back down into my hand with the big cup facing sideways rather than straight up. This causes the string to wrap around and twang the tama and ken together and fall out of my hands. It's really annoying so I'm trying super hard to correct it so I don't get mad at it anymore