I would have hoped that you would have posted whole report on this site. Anyways, it appears that biggest problem of your fight was that you only used ~500pts of your army against whole bulk and elite of opponents army. Your big hitters, KoS and fiends, spent most of their time out of combat and didnt do much. That is very common beginners mistake in warhammer, to play too safely and not fully use all of the units.
Turn two charge from the GG seems wrong and by looking the diagram, majority of them would have been in front and thus should have charged the front instead of flank. There is few points where you could have bought some time, for example rear charging grave guard with horrors would have prevented them from charging your daemonettes. You also kept your KoS badly positioned quite often and didnt predict enemys movements. Try to predict on where he could move and turn him more to get better charge opportunities. Same goes with fiends and seekers there, you could have nailed the zombies and overran to the ghouls with those two units. Fiends could have endured the forward charge and seekers could have helped with flank charge. Just play more aggressively.
Of the army choises, you definately should have picked shadow lore for your Tzeentch herald there as your army is so Slaanesh oriented. Extra levels on heralds are quite a waste of points as level 1 have reallyhard time casting. Also having 5 wizards on your list is way too much, 1-2 is usually good enough. After all, wizards are mostly support, not the main things that kill stuff. You definately should have picked siren songs for your slaanesh models too.
Generally a good tip I would give to you would be, take less characters and more core troops. It is easier to learn to play with less characters and elite and more solid core units fight well and make learning process easier that way. For example army with one greater daemon, one Tzeentch herald with Master of sorcery, 3 core blocks of 30+ and fiends or flamers in rare to support them is very solid base for any army. More troops mean that you can take more casualities and make more mistakes while you still retain your hitting power well with most units. After you get familiar with what all units can do, you can then start adding more specialized units like seekers there. Good luck for your future games =)