Why so much cash on hand? If you're planning to buy a house soon, cool, but considering sitting on $65k is a lot otherwise. The main thing is to have money in the market as long as possible because of compound interest. Toss $50k in, or maybe more. If you have money in after tax funds, you can sell those if you have to in a major emergency. That lets you keep less of a cash emergency fund.
VTSAX is fairly diverse. The holdings information claims over 3500 different holdings in the one fund. That said, if you're seeking more diversity, diversify. I hold a couple other funds, like an international fund. If you have $50k+ to invest, you can open a three fund portfolio to diversify quite easily.
Any particular reason you're planning to throttle back the 401k contributions? At $55k per year, you're probably in the 25% tax bracket, so not paying tax on the contributions seems to make sense. If you're going to retire early, you may be able to take advantage of a backdoor Roth to pay lower taxes on that money. And any reason why $100k is the magic number? Assuming you invest in after tax funds what you would have invested in the 401k, it's all going to be compounding regardless of where it is. The question is what makes you the most in terms of taxes, fees, and fund selection, plus considerations like whether you need to have the money accessible any time soon.
Also, max out the HSA before the 401k. It acts much the same in terms of retirement money, but you can also get money out tax free for medical expenses. That's a huge win, since you'll have to pay tax on 401k distributions and income tax on money going to after tax investments plus possibly capital gains on after tax earnings.