Hello @RoyAzriel ,
If you are going to be experimenting with adding different sensors (Lidar), then Starling 2 Max is definitely going to offer more flexibility due to the larger size and longer flight time.
You should consider the dimensions of the tunnel and make sure that the drone will easily fit. I have no idea how small the cross section of the tunnel is, but if it is very small (just several times larger than the diameter of the drone), then it would be very difficult to fly due to air circulating in a small space.
What Lidar are you considering adding and what is its weight and communication interface?
The illumination will depend on your specific application, depending on how far you need to see. You should be able to add standard LED lights. if you need to control the LED intensity, you would need to get an LED with built in adjustable LED driver and optionally control it using PWM output feature on the ESC.
Are you going to develop your own mapping and navigation stack for this application?
Alex