Okay, so I came up with another idea, but my estimation looks like it is coming up with a smaller handsize than what liopoil is getting so far, so it might not be useful.
I was looking through the card list and found Golem. The friendly splitter that can't split itself. There are some problems. We can't have any non-terminals, because then he becomes a Village. This means, no Scout, no Highway, no Cellar.
With Council Room + Horse Trader tricks, I am finding a max handsize of 51 to start the turn. We have to use up our extra Tactician action to Storeroom away the Horse Traders (because Cellar is out). Now you can Golem into Crossroadsx2 three times, then Crossroads+Necro, Crossroadsx2, Crossroads+Necro, Crossroadsx2 twice.
That gets me to 797260 cards in hand (half Harem). As mentioned, this is lower than the currently discussed solution, so it is no good, but maybe there is something of use here. The lack of cost reduction could hurt this too. (Edit: Can use Quarry for cost reduction, so this one is probably okay)
I'm not sure where we are at on the thing we are buying, and this is only a minor improvement in the grand scheme of things, but I think we can Inherit Death Cart to gain 2 Ruins for every Estate that we gain from trashing Hunting Grounds.