Prophecies, Factions and Nightfall.

My qeustion is this: I have prophecies, and I was wondering if I were to buy say Factions would I be able to take my prophecies characters to factions? Or can you only go from factions to prophecies? Also if I were to buy nightfall, would I be able to take my prophecies characters to nightfall? If I was to make a factions character, would I be able to take him to nightfall if I bought it? Or only to prophecies? Also, if I bought factions, it would add two character slots? If I were to buy nightfall as well, would it add an additional two slots? For a total of eight slots?

yes to all those questions

You can go almost everywhere for any chapter you add to your account. Exceptions would be starter areas for foreigners - a Canthan cannot go to pre-sear Ascalon.

get Nightfall before Factions