I started when I was 15, home sick one day and needed to amuse myself and at some point had an “aha” moment and taught myself how to juggle 3 balls.
Did it pretty seriously for about 4 years. I was decent with 5 balls and could do 6. Never got into numbers with clubs or rings. Torches, knives, tennis rackets, toilet plungers (they are tough, the balance is all wrong), bowling balls and bowling pins. Had a flower stick. Did a lot of chin balancing, I could keep a chopstick on end for quite a while.
I usually preferred beanbags since they don’t bounce off each other and they don’t roll away, I used Squeeze-Its back in the day. Also lacrosse balls (nice weight, cheap, good for bouncing tricks).
Patterns for progress…honestly the cascade is your best starting point, IMHO. All odd numbers work the same way, so learning 5 is just like learning 3, only faster. A couple of tips for 5 - get very good at 3 (consistent throws and catches, you don’t want to be constantly moving around because one hand is always tossing a little forward or something). Practice flashing 3, clap hands, catch, repeat - that will build some speed and accuracy.
Using 5 beanbags, do 5 throws and NO catches - just a nice 1,2,3,4,5 and let them all drop. Focus on good throws - watch where the beanbags land and you can tell whether they’re all on the same trajectory. Go SLOW, there’s no reason to rush the throws, this just makes you inaccurate; make the pace as slow as necessary to get all throws identical, then slowly pick up the pace. Do this a lot, then start adding one catch in (last throw), then keep building up from there. To get used to starting and stopping, hold 5 balls and then juggle three, keeping one extra in each hand.
Another good drill is to have a friend who is learning 5 stand in front of you with his hands out. You do five even throws and he just catches them. Goal is that he doesn’t have to move his hands much (if at all) so you know that your throws are accurate. Then he throws them back. When you’re getting good at this, the interval between his last throw and your first will get shorter and shorter and you’ll be able to constantly run a 5 ball cascade back and forth. I think I got this from Dave Finnigan’s book (also highly recommended, I still have my “first edition” autographed copy on the shelf). He has an excellent approach to teaching which I used when I worked Ren Faires, people didn’t believe me when I said that I could have them juggling in an hour even if they’d never tried it at all, worked like a charm. The whole “do the throws and don’t do any catching” drill is Dave’s and it works great.
Only went to one IJA festival, it was in San Jose in 1984, that was the year that Anthony Gatto (age about 9?) came onstage and just blew everyone away, very inspirational.
Check local colleges, there are plenty of formal and informal clubs, great way to practice and learn from other people. Also check your local YMCA.