My +90 solution required having 10 of everything, so isn't actually possible in a game. But I can at least get +84 legally
Deck: BoM, Procession, Throne Room, King's Court, Rouge, Grave Robber, Coppersmith, Scrying Pool, Worker's Village Watchtower. You have 9 copies of each, 10 of the throne rooms and King's Courts, only need the 1 Watchtower.
Start with WV, Scrying Pool in hand. Play WV, use Scrying Pool to draw all action cards.
Use Throne Room to play KC
First KC play, play Procession -> Coppersmith, Coppersmith, GR (save the coppersmiths)
Second KC play, Play BoM(as Procession) -> Coppersmith, Coppersmith, Rouge (save the coppersmiths, TD with WT)
That plays the coppersmiths 8 times each. The non-Coppersmith cards all get trashed or played but you have four coppersmiths sitting on your deck again and you still have 1 action from your WV. Another WV+ Scrying Pool draws them all and you can repeat this process 8 times for +64, then once more playing six coppersmiths instead of the GR/Rouges for +12 more or +76. You still have 3 spare coppersmiths in your hand. With your final action, use your extra throne room / king's court to play six more coppersmiths. +84. Your coppers are worth 85 and you have 10 buy.
Just need to optimize it by three in order to fulfill "Piledrive 8 colonies with a single copper as your only source of income". Hopefully someone can figure out where my solution is lacking.
So that's +84. With a little more optimization a single copper gives you enough to piledrive the colonies. (Of course, this doesn't generate any buy
