Should I use poly~, polybuffer~, or just copy and paste?!

polybuffer~ and poly~ work great together. Just use thispatcher~, make him send its instance number, and as each of your polybuffer's buffer have a name which is constituted with :
[nameofyoupolybuffer].[indexofoneparticularbufferinsidethepolybuffer]
you just have to use a sprintf to format the name of each buffer, and the number index is the only thing that needs to be changed, adn how convenient ! that's something you can have easily with the instance index coming from thispatcher~. it's like they were designed to work together :)
As for your outs : do you want each instance send its signal to a particular waveform~, at the same time ? In this case, you can use send~ form inside your poly, and set message, which can be depending of the instance as explained above.
if you don't need this, but rather one instance selected at a time, it's not that complicated : you just need to save "set [thisinstancebuffername]" message inside the poly, and output it when it's selected, and send it to your waveform~. Alternatively you could have a waveform inside each poly instance, maybe computer expensive.
And if the overall process is too expensive, you can mute each unused instance of poly with thispatcher~.