Ok, quick updates. I have got 19 gpus to post (finally) with below configurations:
1. 12 RX 5(7/8)0 + 1 standard 1060/1070 (non mining) + 6 P106 mining cards (will try 13 RX + rest P106 when i get my hands on the 13th card)
2. 13 Standard 1050/1060/1070 (non mining) + 6 P106 mining cards.

System config:
1. B250 Mining expert
2. Intel 4400
3. 8GB ram (you need 8gb. With 4GB i had issues mining. Ethminer takes up close to 5GB to mine, claymore not tested)
5. 16GB USB thumb drive
6. CentOs 7.
7. BIOS Ver 1001

Changes to bios - None
Changes to RX card bios - Custom bios to hit 30mhz
Changes to standard NVIDIA cards - None (i dont think bios flash is an option here)
Changes to Mining NVIDIA cards - None

NOTE: The first 6 slots in the board (including the 16 pin) needs to be connected to the mining card (P106). Else it does not work. Also this means we dont need 8 as per Asus manual/website https://www.asus.com/support/FAQ/1034921 .

I am still performing few post install setups, should be done in a day or so. Will post pics of the rig once done. If you guys have any questions, feel free to ask. Will try to guide/help.