Good luck for the project, hopefully you get it and can let us know how it all pans out.
One aspect to consider carefully is the supply access, and if this holiday home would ever be used while the main home owners are away. As it is TT, the SWA will need a 100mA or 300mA delay RCD before it (as well as a fused-switch or similar for OCPD, more to protect the home main fuse and assuming it is 100A otherwise no usable selectivity).
To make sure that delay-RCD is very unlikely to trip you should plan on using a CU that has double-pole RCD on
all circuits. Even cheap dual-RCD boards do that. But given the overall cost already and the benefits of easier fault isolation, etc, I would suggest an all-RCBO CU, but then look for the RCBO that are neutral-switching so you don't end up with a N-E fault taking out
everything. The recent compact RCBO from Fusebox, Wylex, and Crabtree all seems to be DP switching and are reasonably priced.
Don't forget to include SPD. I think some of the CUs come pre-fitted anyway, such as this:
Buy Online Wylex NM906FLEXS 100a Main switch+Type 2 SPD 9 Way Consumer Unit from Edwardes Brothers, 24 Hour UK next day delivery
www.edwardes.co.uk
If the main home is feed from overhead lines it might be worth checking it already has SPD, or maybe making the recommendation that they should consider adding some.