Is it ok to tarmac over an old concrete drive (in reasonable condition) ? This would save a lot of work (and money)

yes its fine. trojan

depends if the concrete is sinking or cracking best to lift first ,or else the movement will continue after you top over it and the tarmac will just crack with it ,if it is sound surface then yes follow lmds advice

Yes it is but you would need to put a bitmac binder on first and then lay no less than 25mm of tarmac