Oblivion start again - questions (also in comparison with Skyrim)

Prehistory:
When Oblivion came out new I got it and just played through the main quest. After that somehow I did not feel like playing anymore because in contrast to good old Morrowind many things displeased me (in-game cities, the level-scaling, the interface, etc). In retrospect, MW would not make fun without mods like "Galsia's Character Development" (quite apart from the MGE or the Replacers). I did not occupy myself with the Oblivion ConstructionSet that was released at the time. At some point I had stopped there with Morrowind, as I once myself have dealt with it, the engine options have been too limited (Auto-Repair, mass battles between div. Fractions, etc.)
Now Skyrim is out and I am also busy playing. My conclusion atm: graphics with a few tweaks nice, wonderful engine (mass battles, lively interaction of all characters, marriages, most extreme selection of escortchars, etcetc.) But what the Gamebalance (Caster without armor hard possible, companion sometimes still badly bugs) or Possibilities of the player rather mau. I do not really like the storytelling and the side quests (after a few quests I'm already the leader of faction Xyz, which usually has only one seat in a city ...) Also, there is no ConstructionSet in sight with which you can do it yourself can create. Since recently the Goty version on Steam was on offer, I have indulged this time, but have not yet installed.

Ask:
Oblivion, like Morrowind, has matured quite a bit, there are a lot of mods and replacers. But before I venture into the risk, a few questions ("technical" / playful possibilities vs Skyrim, possibly realized with mods):

Are there companions and how are they programmed (possibility to adapt equipment, level these in some way), are there various "classes" (warrior, archer, magician or maybe even healer?)
Who massively in Skyrim the civil war quest has done what I mean (faction vs. faction without reference to players possible, also partly between 3 factions) either by engine or possibly even implemented by the DLC add-ons or popular mods?
Trading system reasonable (as opposed to Skyrim * cough * what else in dungeons run when the orbit at the dealer around the corner is available every 24 hours ...)?
Are "looted" dungeons empty or how does it work here? (
Spoiler)
Graphics and story left out, what big "features" do I lose with the Oblivion engine vs Skyrim or do I win over Morrowind?