Open Potion/Silver, really?
You probably won't get a Golem first reshuffle, and may not even buy a Silver every turn first reshuffle. Let's say second reshuffle, so you can play it first turn 8-10. It's a bad Hoard if you only play it once, because this leaves you with 1 Potion, 1 Golem, X Tunnels, X Golds, and you can't buy much else useful. Maybe you play it the second time on turn 11, and then it's starting to get a bit useful. But a Big Money only player will have lots of Silvers and Golds at this point already.
I don't see how this can work at all without support
I tried it a bit, I got my Golem on turn 8, 3, 8, 4, 5, 7 and was totally screwed on 5-2 splits I didn't mention here.
The time I got the Golem turn 3, I got 8 Tunnels afterwards when I had less then 8. I had 20 Golds until turn 20, but only hit 8 once, because all the Tunnels, Potion and Golem got in the way. Only when I got 7 more Golds on turn 20, I started Greening heavily, buying Provinces and Duchies every turn. Starting with turn 21. That's way too late, even with 8 Tunnels being VP as well.
Now Scheme is nice with it, with a first reshuffle Golem, I hit 8 Tunnels and 6 Provinces by turn 18. But the first reshuffle Golem only happens with
33,7% chance. With a second shuffle, I hit 3 Provinces and 7 Tunnels by turn 17, which is good, but not overwhelming. And there are still the times where you are screwed.
Didn't try the other cards you mentioned.
Didn't test how resilient it is against attacks. Might be not hurt this much by Cursers except Sea Hag, though a Curse on the second reshuffle can destroy your chance to buy a Golem, too. I think Militia or Cutpurse are a big problem, though.
So this is a three-card-combo which works great on a 4-3 split where you also hit the 1/3-chance to hit an early Golem and your opponent didn't contest you on tunnels.