Yes you can have more than one companion. You can have a maximum of 300 party points, companions take 70. To get the 300 it would require you to have 10 charisma, good natured, magnetic personality and 300% speech (bit excessive) and you would not be able to have slaves. But it would allow you to have 4 companions, in my opinion it's much easier to just do 10 charisma, magnetic personality and 150-180% speech (with 180% speech you could have 3 companions) and you can still slave. AFAIK ALL companions take up 70 party points although some are superior to others in what they do (Damn you throwing tagged companions!)