Hi fella,the earthing rod is a great system (TT system) but be careful if the ground where the caravans going to be sited is sandy as you may struggle to get a good enough earth,it makes it difficult for the sparky to get good readings to pass it off then and after all it is for their protection.

The readings can be improved by making the ground moist where the rod is inserted but often screwing one rod into another to get down deeper is fine.

6mm cable sounds good to me,2.5 would have been a bit thin IMHO,there's nit a huge price difference either.

There's a lot of shit spouted on forums but people are pretty good on here,I did a caravan live last year by wearing a thick rubber glove to connect it to the mains,I'm still here,common sense really.

The yellow fuse/mcb was traditionally used for immersion heaters which most houses don't really use now hence their usually spare,my garage runs off it in my old house!!!