Go for five group members. Not beat independence.

For a first group, I would advise to have to deal with only three different characters (i.e. all DPS are the same).

If you prefer to go with Paladin+ Druid + 3 x Shamans, go for it !
Druids are wonderful healer (I run one on my PVP team, together with 4 Hunters). Most of the time, only the tank has to be healed (you will still get Healing Totems from the Shamans anyway). Moreover, that will spread the loot (farming 3 of something is ... well, less boring than farming 4 of something), and give you more options for other groups (possibility of having a tank on two different account by dual-speccing the Druid).

Welcome, and have fun !