If I wanted to make my own speaker cables, is this a good choice for wire?

Perfect as is.

I ran this cable against the Silversmith Fidelium and not much in it at all sound wise. Silversmiths had slight edge. Factor in the cost though and Duelund is the hands down winner.

12 guage makes the sound bassier/heavier, and is not as well suited IMHO

Ok then, nice set-up. I did ICs with the previously linked 16awg Jupiter wire, and with Duelund 20awg, both have nice tone and are pretty good overall but are  bettered IMO by my Furutech u-p2.1 ICs.

For SCs, with 100wpc, and depending on the length of your run, you might like the larger 12awg wire mentioned by @needfreestuff .  Duelund makes a twisted pair 12awg in a single cotton casing, just like the 16awg you were looking at.  However if you are trying to buy just one wire to make both SCs and ICs then either the 16awg Duelund or Jupiter would probably be best.

Use connectors from pure copper or silver when possible - plating over the copper/silver is ok. For bananas, the KLE plugs that @williewonka likes should sound nice.  Good luck

I used these BFA connectors in my last build. Crimp and solder.

https://nerveaudio.com/product/silver-z-plug/

Nice work, diy can be an excellent option and parts connexion has some great materials. 

As interconnects, why would you opt for side-by-side 16 ga. wire?  Are you unaware that opens up a world of RFI/EMI pickup?  The Jupiter wire is twisted…a better choice for unbalanced ICs.  For speaker wire, the Dueland might be fine at lengths up to 4M.  Beyond that, maybe go heavier.  For shorter, no need.