Would you tell me what is the difference between sentences of A and B?
If what you want to talk about is the nice feeling of being finished buying a new car—"It's done! I have bought a new car! I have a new car!", you will say something different tomorrow evening:
"It is nice to have bought a new car", OR
"It is nice having bought a new car."
And today you express your expectation of that feeling like this:
"It will be nice to have bought a new car", OR
"It will be nice having bought a new car."