Looking for advice starting Tzeentch, new 40k player

[Rune Keeper]

I'm completely new to Games Workshop, but starting 40k and Age of Sigmar. I really love Tzeentch Daemons and hope to start an army I can use with both games. I'm starting with the Start Collecting box, naturally. I just had a few basic questions about building the army beyond the starter box. I've had a decent number of small games.

First I was curious about Horrors. I'm the only demon player in my area, so everyone has been pretty nice about letting me proxy models to see what I like. I'm not really sure what the best ways to field these are, since there are so many different options between mixing the three types. Are there any popular configurations? Do you like keeping points to split them at all?

Second, I'm curious about HQ choices. I've been using the Herald on a Chariot and enjoy it so far, I wasn't sure if disks or foot heralds were worthwhile. I'm also a little wary of putting out a demon prince or greater daemon. We mostly play by points value, so I wasn't sure if you should only use them at a certain level. Also, can the Lord of Change model be magnetized to let it use either weapon option or be fielded as Kairos Fateweaver? I don't know much about magnets just yet but I'm learning.

Third, since the Thousand Sons don't have a Legion Trait, if I want to use a few can I just slot them into the same detachment with no consequences right now? Mostly I like Tzaangors and sorcerers and spawn, not sure if they mesh well or not with daemons.

Finally, I've only tried summoning a little. If I want to use it is there a particular point value you like to keep set aside per point level? Can Exalted Flamers summon since they are characters (I feel like I'm reading it wrong)?

I hope that's not a wall of text, I'm really enjoying the game so far but don't have a seasoned daemon player to ask these things. There are a few Chaos Marine players glad to have a new player on their side, though :P

[bozo69pd]

Magnus the Red and brimstone horrors. Thats all you need but I would probably pick up Fateweaver just cuz he is cool.

[micahwc]

There isn't any consequence to bringing Thousands Sons since they don't have a legion trait to lose yet. You are correct.

 

I'm not very familiar with summoning since I don't use it; but my understanding is that any chaos character can summon, so if the Exalted Flamers have the "character" keyword they should be able to summon.

[C'rumzoz Plaguecrest]

Seriously recommend the burning chariot. Its quite a beast in damage output