1.5" slicks will really help. Get ones with a kevlar anti-puncture band.
Bike shorts will prevent lots of problems. You wear them without underwear and ALWAYS use a clean pair so get a few.
Gloves not only protect your hands froom vibration but, in the event of a spill, will prevent you skinning yourself.
For more athletic riding, some form of pedal retension system is needed. You can use toe clips (but with loose straps) for a cheap intro. You will probably want to go to a clipless system using proper cycling shoes but take care not to injure your ankle with any system.
Take a basic repair kit (sape inner/patch kit/pump) and learn how to use it.

Get used to riding before starting any serious althetic training .