Can I declare members in abstract class? Should I declare a virtual getter / setter method for the member in that class?

Answer 1

yes, you can, but creation of abstract objects is prohibited (it's possible with some hack, but useless I think)

Answer 2

for real it's easy hack, U just allocate memory which needed for fields of abstract class and then link this memory by pointer of this class x) (when you will allocate memory don't forget about possible alignment of memory)