Usually just one DF folder per release version, no mods, no graphics packs, some minor Init-file tweaking (max pop up a bit, seasonal saves, adding a customised worldgen to give approx 25 Z-levels of largely uninterupted rock between surface/caverns/magma/etc). I may well
The directory df_31_25_win comes out as ~880Mb (just a 5yo Region1 game being played, extremely slowly due to extensive micromanaging issues).
The previous version is under df_31_21_win and is 576Mb (reached spring of 1054, having started in spring 1051)
Prior to that, df_31_19_win had regions 1 (Spr1051->Sum1053) and 2 (Spr1051->Sum1051, must have switched to .31.21 rather quickly in that game) and is approx 448Mb in size.
Looking even further back, I have had up to six regions started, in a single version folder, but these days tend not drag (even where possible) an import from a previous version folder to continue with it under a new one, but tend to fine-tune general concepts and then start again from scratch with some Grand Plan learnt from the previous version. I don't tend to use the seasonal saves for save-scumming purposes (just security of save-data, and perhaps the odd in investigation as to relationship information I may have missed the first time round) Very occasionally I will deliberately copy off the current folder so that I can try something outrageously fort-breaking (e.g. divert everyone I can to mining and abandon all other aspects to see what a particular feature might look like if I spent enough dwarf-hours on it) just to try it out, but most of the time I just integrate that curiosity into the normal running anyway and just take ages over it.