ADD Kyuubi Naruto said:
So ok, I just bought this game, any advice?
Join the Darkside, we have pie...and the better storylines
J/k (mostly)
If you go force, invest in the artifice skill as it helps with making your own sabers. However, do keep in mind that making your own medkits is always a viable alternative.
Flashpoints can be used to gain XP and help buff your light/dark meter. Also your companions aren't light/dark they're more complex than that, however by reading their profiles you'll get a general idea of what appeals to them and why.
Strictly speaking you don't have to be a complete monster or save every single babay. In fact the most interesting storylines generally allow you to be a mix of both (Imperial Agent almost demands this for the most satisfying storyline).