Renovating garden shed, advice?

[juco]

I have dismantled the shed and rebuilding & resiting it.
I have to replace a few planks (tongue & groove shiplap) and a couple of the uprights (wood rot) as the previous owners let it sink into the ground at one corner.
A couple of questions.
1. The old wood has had various treatments/preservatives painted on, and various colours so what would be best for me to use as an overall treatment, it would most likely have to be a dark colour to take account of various other applications from days gone by. The shed will be about 90% old wood and 10% new wood. When it is resited I will have access all round to recoat as and when required.
2. There are some small holes in some of the old wood where there has previously been nails, whats best to fill these with prior to treating the wood. I assume it would be best to fill these.

thanks

 

[foxhole]

Any dark wood fence treatment will do, no point filling holes , will fall out as the timber moves with sun and rain.