hello there.
i am new to the forum and the sport, i want to know hoe advisable it is to bunny hop on a Hopley 20 inch unicycle, should I get a better unicycle? How about small drops? What air pressure is best when doing such things?
Honestly, it depends mostly on your weight. Lighter people (<70kg I’d say) can learn the basics of hopping (up to hopping up a curb) on just about any unicycle, while heavier people will want to move on to something with a ISIS hub and cranks.
Tire pressure: enough to not hit the rim when doing the biggest hop you’d try.
I always was able to drop curbs on beginner unicycles, all growing up, I am now a 180 lbs adult, and still abuse most unicycles.
a light hop was never an issue, only time I waffled a rim, I was hopping off a picnic table with a beginner unicycle.
Long and short, it depends on brand and luck. I would start looking for a better unicycle personally.
Welcome to the forum. For small hops and drops (like up or down a curb or a stair step), you should be fine (unless you’re a very heavy person). As far as tire pressure, a lot of it is personal preference, but you need enough to keep the rim from hitting the ground or the tire rolling sideways when you land. You could start at the recommended pressure listed on your tire and then let a little out and keep experimenting as you lower the pressure. You should also use the search function to find past threads on this topic. This has been discussed a lot, and there’s tons of information out there for you that should be helpful.
Welcome from Costa Rica! One of the many countries I have visited but didn’t get the opportunity to ride a unicycle while I was there.
A “beginner” unicycle will most likely come with a square taper axle (also known as cotterless) and probably a 1.75" wide tire. This is what all of us long-term unicyclists were raised on, because that was all you could get up until around 2000. Square taper axles will take a decent amount of hops and jumping around, but will not withstand it indefinitely. Depending how hard you are on it, eventually the axle will metal fatigue, and one of the tapers will break off. I have unicycles that are 30 years old that are still going strong, but others have broken. And back when I did tons of Freestyle (this was before Trials and Street existed), there was a period when I was breaking an axle every few months.
Last summer, my Track unicycle, that I have brought to most of the Unicons, broke suddenly while I was warming up for the IUF Slalom. Had to finish on a borrowed one. 
That uni (a Miyata) held up for a huge amount of riding before giving up the ghost, and I’m pretty sure that included a good amount of hopping back when it was new.
Tire pressure is basically not a number, because it depends on tire width (how much air volume), rider weight and other factors, which is why we use the simple “enough to keep the rim off the ground” method. For a 1.75" tire, that’s going to be at least 50 psi.
Enjoy! If you plan to do lots of jumping around/Trials/Street type riding, start saving up for a uni that’s made for that. But in the meantime, go ahead and play. You have a good chance that you’ll be able to keep your beginner uni as a backup, and use it to get your friends riding in the future.
My favorite part of Rough Terrain Unicycling is where George Peck sets a half dozen or so stub ends of broken square-taper hubs on a table and says that they’re just “a few of the dozens of axles I have broken.” Later on he says that riding the way he does “will cause stock axle failure in 100 to 200 hours,” which really doesn’t seem so bad considering how intensely physical he was, and he doesn’t seem to be a small guy either. The most talented and aggressive pioneers could hop and jump on the equipment they had for long enough to get good enough to realize that they needed something better.
I try to avoid doing too many hops or drops on my non-Isis unicycles but there’s clearly a difference between the material used in the cheapest of the cheapies and what’s in a better quality square-taper hub. One of the ones George recommended to “reduce failure rates to an acceptable level” was a Phil Wood square-taper hub so it wasn’t just about having splines. Going by the photo, the Hoppley might be somewhere in between. The hub that had failed on my thrift-store 24" Sun Classic seems to be made of particularly soft metal.
With any of them, having a crank even a little bit loose is fatal to the hub. If they were already mounted on the hub when you got it, don’t assume that they’re tightened enough. Re-torque them yourself to be sure. And 25-30 ft-lbs is more than most people guess without using a torque wrench, so use one. A serviceable torque wrench is cheaper than a hub repair and more fun.
Note that at the time Rough Terrain Unicycling was being filmed, splined unicycle hubs you could buy were still about nine years away. The first one came on the DM ATU (David Mariner ALL Terrain Unicycle) which was first available in 1999. KH and other types followed soon after.
Thanks for all the answers
I really appreciate all the useful info. I’m about 70 kilograms so I think I will be fine with my hopping for now. I can’t wait to get a newer, better one anyways:)