There are several options. If you want to replace the existing light
with a fan only and have it work from the same single location switch,
you can do that. If you want a fan plus light, then you have several
1 - Run another cable from the switch location to the fan, though that
can be difficult.
2 - Get a wireless remote, bypass the switch and use it to run the
3 - Get one of the fans that will work both the fan and light off a
single pair. Can't remember if it is Hunter or Casablanca, but one of
them makes a series called Intelli? something that does this.
To support the fan, you either need a metal box nailed to a joist of
similar support or else one of the expanding type box/hanger gizmos
that are made for old work where you don't have access from above.
Regarding fan direction, its supposed to blow down in summer, so you
feel more of the breeze in the room. In winter, it's supposed to blow
up, so that it moves warm air up, across the ceiling, and down along
the walls. However, I think the winter idea is dubious, at best.
Never use mine in winter at all.