It looks like plate #1.
The Arisaka Defense Offset Optic Red Dot Sight Mount is designed to work with Arisaka Defense Offset Optic Plates. Each plate is designed to fit a specific optic footprint. For optics such as the Holosun EPS, you would need to use the Deltapoint Pro plate. For the 508T you will need the RMR plate, and the 509T has a specific plate as well. The adapter plate can be found linked below:
https://www.opticsplanet.com/arisaka-defense-offset-optic-plate.html
The Viridian Weapon Technologies RFX-35 uses the RMR footprint. So you will need the Arisaka Defense Offset Optic Plate at the link below.
https://www.opticsplanet.com/arisaka-defense-offset-optic-plate.html?_iv_fit=trijicon-rmr
The Arisaka Defense Offset Optic Red Dot Sight Mount can be used with a Leupold DeltaPoint Pro adapter plate and allow you to use optics with the Shield RMSc footprint or Leupold DeltaPoint Pro footprint. The correct adapter plate can be found linked below:
https://www.opticsplanet.com/arisaka-defense-offset-optic-plate.html?_iv_fit=leupold-delta-point,leupold-delta-point-pro
The Arisaka Defense Offset Optic Red Dot Sight Mount will be compatible with the Sig Romeo 5 as long as you purchase the T1/T2 mounting plate which can be found by using the link below:
https://www.opticsplanet.com/arisaka-defense-offset-optic-plate.html?_iv_fit=aimpoint-micro-t1-t2-and-clones
Yes, the Arisaka Defense Offset Optic Red Dot Sight Mount will be compatible with the Vortex Crossfire Red Dot Sight. However, you must pair it with the correct Arisaka Defense Offset Optic Plate, which can be found by using the link below:
https://www.opticsplanet.com/arisaka-defense-offset-optic-plate.html?_iv_fit=aimpoint-micro-t1-t2-and-clones
The Arisaka Defense Offset Optic Red Dot Sight Mount will not include mounting plates, it is the base only. The plates can be found by using the link below:
https://www.opticsplanet.com/arisaka-defense-offset-optic-plate.html
There are not any stems to change the height of the Arisaka Defense Offset Optic Red Dot Sight Mount. However, the included stem can be mounted to either have the sight sit at a 45 degree angle or a 35 degree angle. The mounting instructions on the left side of the product page describe this process.
There is not an Arisaka Defense Offset Optic Mounting Plate for the Holosun HS507K. That red dot uses a Shield RMSc footprint, so the Shield RMS Arisaka Defense Offset Optic Mounting plate might work but would need to be modified.
The Swampfox Kingslayer 1x22mm Micro Reflex Red Dot uses the RMR footprint. So the Arisaka Defense Offset Optic Red Dot Sight Mount plate you need can be found at the link below.
https://www.opticsplanet.com/arisaka-defense-offset-optic-plate.html?_iv_fit=trijicon-rmr