It's all the same money - your "house money" doesn't know that it's in a separate brokerage account with 30/70 allocation. If you're 80/20 overall, it doesn't matter if 80% of it is in an account with 90/10 allocation and 20% is in a an account with 40/60 allocation. If you want to go more conservative with your allocation, do it, but putting the money in different accounts doesn't make much difference except psychologically.
If you can really save $140K a year, it seems very silly to just park $100K in cash now - if the market is down 5 years from now you save up $100K in 18 months-2 years. So don't do A.
B is slightly less bad than A, for the same reasons.
C and D are basically the same thing because, as I say above, your money doesn't know it's in a different account! If it makes you feel better psychologically to have the house money in a different account, sure, why not. But think about your asset allocation as a whole.
I'm also saving for a home and what I do is put my non-retirement savings (the savings for the house) in 100% bonds (VBLTX). I'm pretty close to 80/20 overall, but my retirement accounts are overweight in equities and my taxable account is overweight in bonds. Obviously that's not ideal for tax optimization, and it's actually a different asset allocation than I would use if I weren't saving for a down payment (I was more like 90/10 before we started talking about a house), but it makes sense for me right now, because I'm probably going to buy a home in the next couple of years but I'm 8-10 years out from retirement.