My understanding is that conduction bands are energy bands created from the electrons in the valence shells/bands absorbing energy to jump to the next level (is this true)?
Now, do the conduction bands exist even when NO electrons exist in them, and if so, if a cluster of atoms exist together and some of them (or one of them) have a conduction band but the rest don't, does that mean that the conduction energy band exists over all?
Bands are the permitted answers to the Schrodinger equation concerning a periodic configuration of atoms. The set of forbidden answers also form different bands, which we call band-gaps and they of course fall between the permitted answers. Therefore, technically speaking, we have infinite number of bands as well as an infinite number of band-gaps. Now, when we try to fill these bands with a certain number of electrons (just like filling something with water), it gets filled up to a certain height. The last filled band is called the valence band, and the first empty band is called a conduction band.
This is just a matter of naming some of the more special bands, because we tend to focus on them more often. We usually don't care for the 10th empty band, because nothing important happens there. Therefore, to answer your question, if there is no electron present, these names don't make much sense and you can call the bands however you like!
The bandstructure including conduction and valence band stems from the periodic potential created by the nuclei. Since it depends on the species and particular species have a certain number of electrons, an "empty" electronic bandstructure does not make too much sense. Electrical transport can only take place in partially occupied bands, as electrons or holes need to move and therefore need a free state to go to.
Yet, if you like to think in these caregories, look at photonic bandstructures. The really can be unoccupied.
