Maybe not NTSC but I did look into it a few years back after a conversation on IRC (there are a few xbox isos that are harder to come by and we then ran the numbers for a few systems). The number I got back was realistically doable but would have warranted some special measures (if something all fits on an external drive I can order from anywhere then it does not bother me, if I have to span it across multiple drives then I have to consider redundancy properly.
Equally what are dealing in? Wii games used full disc encryption so 4.whatever for the plain dumped and unscrambled iso then multiplied by the number of titles + sub revisions where they were a thing + a bit more of the dual layer (35 across all regions according to
http://www.abgx.net/filename/?ch=8&...&bin_search=dvd9&bin_search_results=0&x=0&y=0 , though a few of those will go as they got nuked). Equally why just NTSC? There were some notable exclusives outside it, and possibly some enhanced versions (usually is for all the other systems but I am not sure about the wii at this point). If nothing else if you are going to include all the crappy sports games then you really should do those as well.
Going by the ABGX list for the full whack and assuming 4.35 gigs then just under 18 terabytes. Just under 10 if you do restrict to NTSC only (maybe a bit less as that does not account for the nukes). The wiiware text list does not include the size component though (the main site did but did not allow full listing) so I did not bother with that.
Scrubbed and compressed would drop that somewhat, though proper preservation for possible future systems (said xbox isos often had to be redumped to work with the backwards compatibility of an unhacked 360) would demand the padding be kept in some form (you can always patch it back in later) and being encrypted it it not likely to compress. Assuming you are willing to skimp there then for that I would probably look at one of the USB install size lists and sum the table. I don't have such a list though. I would also want to add wiiware as there were some good things there which never made it outside it. For VC I would probably only pick the notable changes or ones where they got translations where before there were none.
That said I can apparently buy a 6TB drive off the shelf today so I reckon you could probably do a complete NTSC + other notables scrubbed collection on a single drive if that is where you were heading.
For the curious I also wandered over to a torrent site
Code:
Atari - 5200 (20081124)
Atari - 7800 (20130121)
Atari - Jaguar (20100525)
Atari - Lynx (20101028)
Atari - ST (20120212)
Bandai - WonderSwan (20101126)
Bandai - WonderSwan Color (20090531)
Casio - Loopy (20090617)
Casio - PV-1000 (20100525)
Coleco - ColecoVision (20100822)
Commodore - 64 (20090416)
Commodore - 64 (PP) (20090507)
Commodore - 64 (Tapes) (20090416)
Commodore - Amiga (20111115)
Commodore - Plus-4 (20090105)
Commodore - VIC-20 (20090106)
Emerson - Arcadia 2001 (20081124)
Entex - Adventure Vision (20081125)
Epoch - Super Cassette Vision (20100525)
Fairchild - Channel F (20081125)
Funtech - Super Acan (20100527)
GamePark - GP32 (20100224)
GCE - Vectrex (20081109)
Hartung - Game Master (20081125)
Magnavox - Odyssey2 (20081127)
Microsoft - MSX (20111129)
Microsoft - MSX 2 (20111129)
NEC - PC Engine - TurboGrafx 16 (20121016)
NEC - Super Grafx (20110307)
Nintendo - Famicom Disk System (20110212)
Nintendo - Game Boy (20120501)
Nintendo - Game Boy Advance (20120512)
Nintendo - Game Boy Color (20121030)
Nintendo - Nintendo 64 (20120427)
Nintendo - Nintendo Entertainment System (20121027)
Nintendo - Pokemon Mini (20081130)
Nintendo - Super Nintendo Entertainment System (20121028)
Nintendo - Virtual Boy (20120206)
Philips - Videopac+ (20081108)
RCA - Studio II (20090104)
Sega - 32X (20110728)
Sega - Game Gear (20120814)
Sega - Master System - Mark III (20120417)
Sega - Mega Drive - Genesis (20120901)
Sega - PICO (20120922)
Sega - SG-1000 (20120425)
SNK - Neo Geo Pocket (20120228)
SNK - Neo Geo Pocket Color (20120227)
Tiger - Game.com (20081125)
Tiger - Gizmondo (20070531)
Watara - Supervision (20081124)
VTech - CreatiVision (20081127)
All in apparently clocks 21.83 GiB (23437324169 Bytes).