Pole Mounted Transformer

It is highly recommended to have surge arresters at the terminations where the underground cables connect to your overhead cables at the riser poles. The arresters at the transformer are there to protect its windings, and may not even be on all the phases (depending on the transformer connection to the line). The best place for protection is nearest to the equipment you want to protect.

I can't see the sense in having the two terminating poles just 5m apart. To gain enough cable length the cable needs to be cut and the poles sited far enough apart to allow the cut ends to reach the top of the poles, otherwise your going to have to have an underground joint.

there is going to be 2 inline joints plus 2 o/d terminations

Re-think how you cut the cable, it can be done with 1 joint and the 2 pot heads. To me UG joints = problems.

PS, I trained as a jointer!

You definitely need surge arresters at both end terminations; specifically heavy duty Riser Pole that are designed to protect underground cable circuits.

Let me emphasize why surge arrestors are required. Normally the use of surge arrester is to protect the equipment from lightning surges.Now we put surge arrestors on overhead lines because where we find the overhead line in rural area, means no building or construction with a height more than the height of overhead line, there are more chances of lightning on that particular overhead line. That lightning surge will travel through that overhead line, which will result in conductor breakdown OR overhead line accessory failure. Now, when you use cable for feeding PMT there are no chances of travelling lightning surges through the cable.(Chances are less, when there is a shorter length of overhead, though it depends on surrounding area) Yes, it is required to provide surge arrestor before PMT. In addition to that, the earth you provide to Surge arrestor should be separate from PMT body/neutral earthing.