You can be whatever you want. What "Class" you chose at the start only gives you some kind of weapon (hardly matters really with which one you start), and a skill that belongs to that class. Now that the ranger starting skill isn't actually very good so just as an advise you should pick something else even if you want to be a ranger (theres a thread about character optimization if your interested).
Yes, there is no priest trainer, but again it doesn't matter since the trainers only give you one skill at that class. Everyone gets a creature (after a related quest is completed). You can customize your creatures and you will learn about it quite early on (and later will be able to finish the quest). The creature is not related to the priest tree if thats what your worried about.
Also, you can have a creature and 1 summon active at the same time.
