Personally I would use a cash reserve like that to say “Fine, I am free of the need to grind or otherwise fund my account for at least a few months, time to check a few things out”.
Depending on the skills you have already accumulated, you might go Alpha for a couple months, or Omega up and start working on some skills for the following:
I would get a good sized hauler, stick enough ships/supplies in it to carry about 10-20 smaller ships, then:
- Take 20 ships over to Faction Warfare and just go a bit crazy, see what I can shake loose.
- Fit out 10-20 decent exploration ships, fly them to a good jumpoff point, try some exploration
- Fit out 10 decent WH anomaly combat site ships, try a bit of WH delving
- Fit out 10-20 fun but cheap solo PvP ships, fly them somewhere close to low sec and try a bit of lone wolf hunting
That entire process shouldn’t cost you more than 10-50 billion. Maybe less if you stuck to cheap/disposable builds. Probably take you about six weeks and should cover most of the active/interesting areas of the game, as well as give you a feel for what direction you might want to head in next.