20 AWG is awfully thin, not thick. 10 AWG is awfully thick. Can you even get such wire connected to your amp and speakers? Soldering plugs onto such wire is a challenge in itself.
I would suggest you get 14 AWG wire from monoprice.com
Regarding gold plugs, the only benefit will be in reducing oxidation over the years. Sonically, there will likely be no difference whatsoever, given that your system won't be able to reveal any (no offense).
Hope that helps.
Best - MM