i have another system with 64 GB but both systems only use about 14 GB or so, which means 16 GB would definitely be too tight but 32 GB enough for the next 2 or 3 years IF you have the option to upgrade after that 3 years or so.

as for video memory my system with RTX4080 16GB is using about 5GB video memory in just normal heavy use ( google maps 3D, photoshop, youtube, all open simultaneously but no games running ). i would put 12 GB video ram as bare minimum for a new system.