The sold 08 Sprinter had more lighting than necessary so reduced the number of lighting fixtures in the Transit. Bought the 2015 Transit optional LED lighting. There were two lights above the rear doors and two in roof near slider door. The two above the rear door each had a plug and the two midway on roof are on one plug. Believe the LED lighting is now standard. The LED lights are very bright. Some may think they are too bright to use in a conversion. Problem with the cargo lights is Ford did not provide a method of turning lights off if cargo doors were open or on if cargo doors were closed. Dumb. Many have modified the Ford wiring to add switching. I simply unplugged the lights from the Ford loom and reused them powered by the house battery and installed on/off switches. Used one of the lights centrally located above the rear doors with a on/off switch located next to the light. Built a box enclosure above the doors and located the light on the bottom of the box. Used another of the lights above the shower and have an on/off switch located high on shower wall. The sink cabinet is located at the slider door and has two of the lights above the sink with the on/off switch located on side of sink cabinet that faces the front of the van. The sink light switch can be reached when using the sink or from outside before you enter the slider door. The four original Ford LED lights are the primary lighting.
In addition to the Ford LED's there are two strings of LED lights located in the bottom slot of the 80/20 extrusion above the bed platform under the two overhead cabinets. Each cabinet has a switch for the string lights located under the cabinet and reachable from bed or from the aisle.
Also bought a flexible stem 12 volt light that can be plugged into a 12 volt socket that has a switch on the light. This portable light can plugged in at four locations. There are sockets at the end of the bed platform on both sides of the van centered on the bed platform. Light can be used as a reading light while in bed. There is a socket on front side of the sink cabinet where the light can be used when using the fold up table off sink with passenger seat rotated. Light can also be used in one of the dashboard 12 volt sockets. Could not find a plug in light with a long enough stem for the end of bed location. Made a 12" long extension from 1 1/4" schedule 40 PVC pipe. Bought a 12 volt extention cord from Harbor Freight. The female end of the extension cord press fit into the pipe ID. Coiled up the cord and stuffed it into the pipe and just had the cord male end sticking out of the other end of the pipe. Used a short length of rubber hose to adapt the male plug OD to the pipe ID. The extension made the light tall enough to be used at the end of the bed.
There is also a large LED light located in the sink cabinet facing out. This light can be used to illuminate the area outside when the slider door is open. The light switch is located near the light.
I think most conversions (including my first one) have too many lights for the small space. Many use a central switch panel with all the light switches in one location. I believe it is much more convenient to have the light switch for each light located where you will be standing when you want the light turned on.