So I can ride almost a third of a mile without getting off and freemount reliably now. Yay!
What next?
My main goal is to be able to ride the trails behind my house, so I’d really like to be able to hop. Seems hard, though!
My question is, do I need to learn to to idle before I can learn to hop?
Also, if anyone would like to suggest a hopping tutorial that was particularly helpful to them, that’d be great. I’ve found a couple, but I’m still having a tough time.
I learnt to hop way before I could idle so hopping for sure. 
Hopping will be easier to learn. Well, at least beginning hopping. Just start trying it. It seems hard at first, but you will make progress very fast. Idling is a great skill to learn and it will help your all around riding a great deal, but it takes time to develop. Start learning both.
For hopping, you can ride up to a wall or something to keep your balance and try just one hop. Soon thereafter you will be able to do 2, then 3, 4, … After a few days you’ll be doing 20 or more. Then start hopping up curbs, down curbs. Then begin working on rolling hops over cracks in the sidewalk, then rolling hops down curbs, then rolling hops up curbs.
For idling, just practice riding, then stop, and ride away. Then ride, stop and ride back a half rev. Then ride, stop, back a half rev, then forwards a half rev, and ride away… Once you can do this, start adding more back and forths.
If you just browse in the articles & tutorials section of the forums you will see plenty of threads about hopping and idling.
For muni, hopping is much more useful. I can idle decently on my trials, but I can’t idle on my muni. 
I found hopping pretty easy to learn, it was just a matter of trying it. Much easier than idling. 
I also find it easier to stillstand/hop at say intersections when waiting for the light to change than it is to idle.
I’d say idling. This only because idling takes time to learn, and hopping essentially doesn’t. It’s a no-brainer. Once you figure out how to keep your feet from letting the pedals turn, you’ll be doing it within minutes.
So work on the idle (and the freemount, if you haven’t got that figured out yet).
I could hop before I could ride, I still struggle with idling.
John is probably right, but my advice would be just do whichever one feels more natural. Hopping would be more useful for MUni though.
hopping up on stuff is really hard
Don’t be fooled by the amazing vids of Scobro and others. As a newish rider myself, who rides with no leg protection usually (to hot), hopping is mostly a way to turn around in a tight spot. I think the hopping vids are great, I am just saying don’t expect it to be as easy as some of the better riders make it look.
Idling can be learned while watching movies or TV. Just keep your uni handy and use it like a chair. Difficult at first, you can just sorta make it up as you go along. For me it is kinda tiring, unless I compare it to hopping, which is really tiring.
The cool thing about idling is it helps to set yourself up to hop or ride backwards. It is the skill that you can use to develop the balance you need to do hop-ride transitions or to start riding backwards. So I would say start idling while watching a movie. Learning to idle makes the other skills a bit less intimidating.