If Ai-chan has unlimited funds? Ai-chan will build a spaceship. Ai-chan will go build a farm on Trappist 5. Because traps are delicious.
A hero banishing circle so people can liveout their isekai fantasies and to migrate to uninhabited planets. A respawn point for unexpected accidents (and a save point feature only I can use). An underground lair full of useful gear complete with a superhero team. A cold fusion reactor to produce power for everybody. Free virtual reality centers and servers for anybody to play a variety of virtual reality games. And a few other things but those would be kept secret and personal. An unescapable, incorruptable hellrealm that perfectly judges and punishes sin, for criminals. Other realms and afterlives will be built to act as heavens. A mad scientist style lab because that could be useful. A wall armed with advanced weaponry that surrounds the place keeping invaders of all sorts out with extreme prejudice aided by a powerful magic circle. Also a safe waterpark and theme park, that is completely free. With the infinite resources gained from cold fusion and other worlds I will recreate the stores to give away free things instead of requiring money. And build a lot of casinos partly as more entertainment but also because the mouse utopia experiment makes me weary of making this society too perfect.
I would build nothing, because the consequences for spending the amount of money needed to improve the world to such a degree that happiness is universal would be crippling. The premise promises much good, but reality has limits, and I expect that I wouldn't be able to handle the guilt for bad things happening while I try to pave the way with good intentions. Doing good is fine and dandy, but I'm not the right guy for the job.
I'd make Lake Tahoe into pumped storage and a portion of the San Joaquin valley in to the reservoir. Then i'd build high voltage underground DC power lines to feed energy to and from the rest of the country. This would easily allow us to kick non-renewables and also nuclear without needing to use peaker plants to supply energy at a frequency of less than once every 10 years. The amount of potential energy in this reservoir (presuming we dammed the walls of the lake up a bit) would make this true even if our population grew and the energy that we use for fuel-based vehicles was instead used as electricity (which isn't plausible given how much more efficient electric vehicles are). Then the greenies could hopefully stop hyperventilating and the powers that be would have one less avenue to enslave us with.