Want to invest. What's the best way to go about it?

Background: I'm 20yo, graduated college with no debt this year thanks to an incredible scholarship, community college, and my lovely parents (and some of my own work :)) I also estimate not having to pay for grad school, which I plan to go to in about 2 years for either 1 or 2 year programs, but I'm still considering a part-time/online program. If I choose to pursue grad school full-time, I will be receiving a stipend. I have a job that contributes to TSP at 5% matching, I currently have it set at C/S/I/G/F : 50/35/12/2/1 % After all expenses (about USD$2407/mo =rent, utilities, health insurance, groceries, minimal going out etc – and YES I know it's a lot of $, but my income allows it and I live in a crazy expensive area) are paid (in full, always) I have about USD$750 "free money" left per month. I would like to invest it beyond TSP. Yes, I have looked over the FIRE chart, but I'd like more feedback. In addition, I'd prefer to have some liquidity as I'd like to make a down payment for an apartment/house in about 5-7 years, preferably resulting in limited (if any) debt/loans (let me be optimistic..) Give me your best, most-tax-efficient advices :) Thanks! \*p.s. this post is posted to various subreddits because I would like to max out who is seeing what.