I agree with a lot of the feedback you've got already. However, I wouldn't recommend Lee Sin for a newbie jungler. While people complain about him being straight up OP, I think he actually has quite a high skill cap for a player who will be focusing more on figuring out how to actually jungle, rather than implementing constant ganks.
I'd suggest champs like Rek'Sai and Warwick for you right now. Both have good sustain in the jungle, so making mistakes is more forgiving. WW should only really gank at 6 or beyond unless you have red and you're confident in your laner's hard cc and damage. Rek can gank at any time, but preferably after you have all 3 of skills unlocked. With either of these two you can focus on figuring out your farming phase (first 2 jungle clears or so), and then consider if you want to show yourself for a gank.
Rek'sai has more aoe cc and global map control (if you leave tunnels everywhere and are good about checking your minimap), and ww is kind of a one trick pony with his ult (which gets countered hard with any kind of enemy cc). That said, ww sustain (if you can keep a focused aa target) makes him deceptively tanky, and enemies can blow a lot of their dmg and spells on you trying to whittle you down, which is its own kind of utility. If you can wait for known hard cc to get blown, or find yourself in a duel, you basically get a free full ult off, which is fun and satisfying. The most fun thing to do with Rek is to loop through the enemy jungle at lvl 3 and plant a ward to make sure you don't get surprised by the enemy jungler. Then you can tunnel from behind the enemy laner(s) and gank the hell out of them from "out of no where". The most obvious way to do this is if you are blue side (bottom of the map), and you walk into the enemy blue buff area to the enemy "tri-bush." You can then tunnel from that bush into the bottom lane from behind and use unburrow to knock up one or both bot laners and almost guarantee an early kill. Top lane is also eminently gankable using a similar strategy.
Good luck!