Days will be short in January. Here's a link for the average weather: holiday-weather.com/vilamoura/…
It's quiet here in wintertime as Vilamoura does only have 2000 residents. I suggest you hire a car because it's excellent weather to go out and about.
A website to further explore: http://www.visitalgarve.pt/#
you will find a monthly program covering all the algarve
Also worth looking at the Downloads, under downloads/other publications you find a guide "guide to trails" for walks.
the guide "rotas/tours around the Algarve" for scenic drives.
Vilamoura has a nice Roman museum, at the West side of the marina.
Edited: 11:17 am, December 14, 2012