Aurora R10, how many M.2 drives can fit?

There's only one M.2 slot. If you want to add more M.2 drives, you'll need a PCIe M.2 adapter card.

With that existing config, I would suggest you just add a 2.5-inch SATA-3/600 1-TB SSD.

It's inexpensive, and it's much faster than any spinning HDD ... plenty-fast for the kinds of things you would be storing there. 

OK, so where do you obtain this drive you're talking about?

I have added a M2 drive using a adapter. I used this adapter to put it in slot 4 https://www.amazon.com/gp/product/B07JJTVGZM/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1.

Ditch the spinning rust!

I too have a PCIe riser card and 1TB Samsung EVO NVMe as well as one Samsung EVO 2TB SSD.
I removed the cage for the 3.5" to provide a bit better airflow at the front. Might put in a second fan.

I also have 2x 1TB M.2 NVMe (Samsung 980) drives in addition to 10TB sata drive for large media/files (photography hobby).

Slot 1 of PCIe is for GPU

Slot 4 i use for the NVMe riser card w/ NVMe

Used this card

Amazon.com: GLOTRENDS M.2 PCIe NVMe 4.0/3.0 Adapter with 0.12 Inch Thick M.2 Heatsink for M.2 PCIe SSD (NVMe and AHCI), PCI-E GEN4 Full Speed, Desktop PC Installation (PA09-HS) : Electronics

You also have 2 x 2.5 drive bays that you can add regular SSDs as well.

when i try to open up my killer control app it tells me its not running, just a black window with those words in it appears any idea how to fix?

did this affect gpu performance at all?

Yes it will.  I added a 2tb m.2 in pci adapter to SLOT4. It cut my 3090 from x16 4.0 to x8 4.0.  Wish I'd known this before hand.  I'm probably going to order a 4tb and just replace my on board 1tb and the 2tb adapter with one drive.

The top SLOT1 on the Ryzen mobo is X16 mechanical / X8 electrical without any M.2 adapter in the X4 slot.