The problem with croatian islands is that there is a very few connections between them. So, I suppose that Pag is not the best starting point if you wish to visit many other islands. As I know, Pag has connection just to Rab with catamaran and, occasionally, with small boat from Lun. Also, there is possibility to go to Olib & Silba with private touristic boats (one day trip for about 30E/person).
Perhaps, better possibility is to visit Krk (bridge) with very good ferry conection to Cres (for cars, also) and from Cres, over the bridge, to Lošinj. From Mali Lošinj you can go to Susak, Srakane and Unije (one line for all of them) and also you can visit Ilovik (all of that for pocket money but without car). That will be, as I know, all.
About accommodation - if you go in high season (july and august) there is possibility to have problems with overbooking, especially on small islands. So, I will recommend you to book in advance. Try to find some private apartments on the net - it's easy because of many of them.