Congrats on the lifestyle progress and welcome! I am certainly not the most knowledgeable so hopefully others will chime in, but maybe these answers will help direct your research:
1. As long as you're ok with no bonds, those are two fine funds. It looks like the Admiral shares expense ratio is the same for both as the equivalent ETF's, so I don't see any advantage for one over the other. (Actually, I believe the mutual fund will be more subject to capital gains due to sales within the fund, but I can't expound on this....someone want to chime in?)
2. You're only ever taxed on realized capital gains, which only happen when you sell. For buy-and-hold, you won't have capital gains until you rebalance, retire, or have to sell your taxable funds to max a sheltered account or fund some other expense. See this thread for how to allocate your investments to minimize tax liablity:
https://forum.mrmoneymustache.com/investor-alley/investment-order-65299/3. As total market funds, both of those will pay dividends. Vanguard will let you set up a DRIP to reinvest the dividends commission-free. This is an option when you open the account or can be started later by giving them a call.
4. If you're contributing a few grand each month, a good chunk of that probably won't be tax advantaged and you'll have to pay some tax on it. While there' some discussion on here about safe withdrawal rates, its usually on the side of being less than 4% rather than greater. Also, that's 4% each year, not each month hahaha. If only it was that easy! But you'll have plenty of time over the next ten years to refine that math, test assumptions, and figure out the more advanced stuff. Again, welcome and good luck with the savings!
Edited for the capital gains difference between mutual funds and equivalent ETF's