A ninety-year-old house was built with stones of a format no longer in use today. In addition, they are probably still solid, so they are no longer structurally suitable for walls according to today's insulation standards; decorative, yes, but even there the different format causes complications. They are therefore more suitable for horticultural uses than for the house again.
Old wood is welcomed and in demand in the renovation of old buildings. But if you don’t have the right connections, you can still search a long time for buyers.
In general, I find it nice on the one hand when someone wants to do demolition not by smashing things up, but in a way that preserves materials. And secondly, you partly have to do that, since mixed (especially contaminated) construction waste is expensive to dispose of. But that is also labor-intensive, meaning if you don’t do it yourself, it is costly in terms of labor.
I would (following the motto of ten commandments / three treasures / what would I take to an island) make a strict selection of appealing things, deliberately preserving and expanding only these, and let the rest follow the path of all earthly things. Unless you have a lot of time and money.
Depending on (also structural) quality of the substance, what I would consider is: to what extent it might be economical to leave the old basement under the slab of the new house, possibly with relocation of its exit. However, the architect must really love his job for that.