Firstly, you should give strong consideration to playing Rome 2 vanilla before trying any mods. The base game has seen significant improvements and enhancements from its launch days, and you will need to understand the base game's mechanics (buildings, food, economy) before you are ready to try more advanced mods. The DLC's themselves are actually quite enjoyable on their own and some (like Empire Divided) do provide new mechanics (banditry) that are also present in DEI.

Secondly, I don't know if the DLC's (Ceasar in Gaul, Empire Divided, Hannibal at the Gates) are required for playing DEI and PB, but I do know that DEI does offer compatibility with most of those DLC's in its base form.

Thirdly, I haven't played PB, but I can say that DEI is very much the "next step" for those seeking immersive and realistic gameplay. The population and supply line mechanics really do force the player to manage wars and provinces with a lot more care than in other versions of the game. You cannot steamroll through entire campaign theaters as you grow bigger in DEI, because you constantly have to ensure your forces are positioned for resupply and reinforcement. Some people find this mechanic annoying; personally, I welcome the challenge as being able to recruit legionaries in freshly-conquered provinces to continue your armored blitz krieg just isn't enjoyable for me.

Strongly recommend you play vanilla first; afterwards, try DEI if you want realism and more difficult gameplay.

Do not play without any mods at all though, because the game is, like all other games in the series, broken without community patches such as Ultimate Fixes, Eastern Overhaul, aqueducts fix etc.