Exterior Light wiring entry to house

Hi,



I installed a post light using 1/2" pvc piping with THWN wiring. I would like to install a photocell but I don't really want to install it on the post. I would rather install it on the box where it enter the house. My photo cell requires a 5/8" hole for the sensor and the body of the sensor (inside box) is about 1" deep. I will be running the wire into my garage where I have romex coming from the breaker panel.



So my questions are-



1. Using a Type LB box to run through my garage wall, do I make the connection from THWN to romex inside the LB box?



2. I would like to install the photocell in the box. However, a type LB box may be too small. Can I use an FSE(single entrance, single gang) box? I would have to drill a hole in the back of the box to run the romex inside and use a blank plate but I don't know if this meets code. I don't see why not as an existing metal box on my house has a hole in the back for the wires (no nipple). If not I suppose I could use an FSC(double entrance) box to house the sensor and then run conduit to the LB box to enter the wall.



3. When using these boxes I noticed they don't really have any method of securing them to the wall. I noticed an existing metal box on my house has external ears for screws. Can you just run screw through the inside of the box?



Thanks

Exterior Light wiring entry to house