I dont know who to buy next, here are some of the ones i dont have. im leaning towards 
then 
but im not sure about it. I try to play assassins but i screw up relentlessly, and i just personally like mages better.
Like 3 or so of who to buy would be helpful. i plan on testing malzahar and kennen soon because they are free.
I dont know if this helps at all but my current favorite mages are 
and
You seem to like long ranged immobile poke mages that can self peel against divers. Xerath is THE ultimate long ranged poke mage that is almost impossible to dive.
Malzahar's space-aids is always fun to use. Put it on minions and it gives you mana each time it spreads, put it on enemy champions and they are going to take a lot of damage that they can't dodge.
I dont know who to buy next, here are some of the ones i dont have. im leaning towards
Dude, just pick whoever you like. The most important thing is that you enjoy playing the champion and in general, players tend to play better on champions they're comfortable with.
I would recommend Leblanc, Ahri, and Lissandra. They are very powerful if you can play them right. Out of you favorites, I would narrow it down to Lux, Kennen and Brand. But the recommendations I think fit what you want much better
I'd say Xerath and Ziggs, going by how you seem to like Lux. They retain the long range you might be used to, while adding new strengths as well.
Ahri is a good blent of mage and assassin.
really poking team compositions are really starting to shine in the meta and champs like xerath and ziggs along with kog ma or Corki (ADCs) really excel in dishing out long range damage for securing towers and defending your own.
Diana is also someone i really like while she has a lot of poke with her Q alone with her all in pressure and damage at lvl 6. She really similar to Akali in the way she power spikes and plays.
I'd narrow your choices down to and .
