Earlier quoted context omitted.
Open a taxable account at Vanguard and invest however much you want in VTSMX. Done. For extra credit, switch to VTSAX once you get above $50K.
What are the pros/cons of the various Vanguard options? I'm in VTI (TOTAL STOCK MARKET ETF) and VXUS (TOTAL INTL STOCK INDEX FUND ETF) because I believe that's what it's suggestion thing said to me, what's the comparison to VTSMX? And what's the difference for VTSAX at 50K?
Having some international exposure is fine too and diversifies a little, but historically, as long as you don't sell off during a lull in the market, the US total stock market has performed admirably as long as you can hold your shares at least a few years.
VTSAX is the "Admiral" version of VTSMX. Same index, but cheaper to own (they take a smaller amount out of it every year for management fees.)