I play a ton of HH, so ill try to help you out!
Firstly, check out some youtube videos to figure out the basics like how the songs work etc. This one is pretty good:
https://youtu.be/dpy8rP9946Y.
The link you mentioned seems fine. Only new thing is the self improvement buff, which makes you do more damage. Basically keep that up at all times.
Good horns to start with are the heavy bone horn or the ore horn while you work on bigger stuff, both work against pretty much any monster and have good buffs. The neirgigante horn is excellent for general late game use, as is the bazelguese one.
Teostra horn counters val hazak, and the xeno one counters kashala daora but it alright in general. Kirins horn is good against kirin as well.
You want to mainly be aiming for the head while building up songs, then using them during openings to get some good damage+stuns in. Your main damaging combo will be forward+ song (the kick one) then hold back for the encore (the triple swing). It takes a long time so look for openings or safe places inside the monsters hitbox. Holding different directions during encore will let you hit a target that moves a bit easier. Eventually youll find the spots you can do a full combo in even while the monster is attacking.
Constantly refresh buffs, even if they havent expired yet. If something like earplugs or ailments negated expires at a bad time it could cart someone.
You can roll out of your songs after the buff applies or right after the damage goes off, as well as between the song and the encore. This is super important to do, as you'll be locked in an animation if you miss the window and probably get smacked.
For build I just do standard damage stuff, but if you want to go super supporty you can build defensive. If you want to use it solo bring damage though.
Generally you dont ever want to play a full 3 songs at a time unless you're buffing before a fight. You waste a ton of damage potential and lock yourself in place for a very long time. I tend to individually play and encore (if possible) each buff into the monster to maximize damage and minimize the time spent building up songs.
Hopefully that helps a bit.