From my point of view: which wiiu games do you want to play? It has some great games, but I cannot deny that most of them are mere enhanced abilities of games that are also available on the wii (e.g. New Super Mario Bros U is a nice game, but for nostalgia sake, gameplay is barely different from SNMBwii). If it's just for nostalgia sake...I'd go for the wii.
(note: if at all possible, avoid the "family wii" edition, as it lacks gamecube controllers. And if you want to hack it at all, avoid the wii mini AT ALL COST).
This is purely for the hacking part. Let's see...
For hacking, the very minimum you will need is an SD card and some time to read up on some basic principles on hacking the wii (it's been a while since I checked, but modmii is an awesome step-by-step tutorial that'll get all the files you need as well as the info). It's advised to invest in a dedicated USB drive, as they generally allow for way more storage room than any SD card (some pirates store pretty much the entire wii catalog on it).
On the wii, all hacking can be done with letterbomb or bannerbomb, which utilises an exploit in the wii interface (meaning: no other things need to be purchased). On the wiiu, these exploits don't work. However, a handful of wii games have similar bugs that can be exploited to install the HBC (which serves as the starting position for roughly anything else). So you'll need one of those (Super Smash Bros brawl is the most common one, though there are a few others).