My mind tells me to put $15,000 on S&P or Dow Jones index fund. And use the $5000 for other things you like - travel, etc. But if I was at that age, my emotions tell me to get a Sports cars and do a road trip . Seriously, invest the money, so you can be a millionaire at 60 yrs old.
3. Don't look except as required at tax time for at least 20 preferably 30 years. Then but the appropriate life cycle fund for your /situation.
Party on, do life, make your good moves/mistakes just like before you ever saw /heard of the money.
heh heh heh - at age 72 hindsight says I did best in the 401k(Bogle's Folly) I never looked at that much nor messed with - doing nothing was my best investment move and I made a lot of less stellar ones over the decades.