in previous ES titles I am allowed to go wherever and explore whatever, whenever I want. will this game be more quest focused? will I be able to explore area's (caves, barrows, etc.) wether or not I have a quest? will I have to have a certain quest to enter certain area's of the game? is it an open game world? will I have to complete certain quests in order to progress to other areas of tamriel?

From what I hear, you'll only have access the lands your faction occupies. If you're with Ebonheartn, you'll explore Skyrim, Morrowind, and Black Marsh.

Since it's an MMO there will be a slight more quest focus, but you are certainly not limited to your factions zones, there is 50+ and 50++ content that allows you to enter all the other zones once you've completed your respective faction area.
In terms of explorability, obviously there is some limitation due to enemy levels and scaling, but they've said you can explore all over an area, searching caves etc to discover new quests/items that you wouldn't of found if you only focused on the main quest.

Being an MMO where creatures have levels appropriate for their area --- that is, they don't scale to your level as they did in other TES titles --- they almost have to have some kind of quest mechanism to gate access to too-advanced areas, or else they'd never hear the end of it when people face foes way too powerful. That said, I wouldn't mind LETTING people explore to their hearts content and getting gaffled by foes because they skipped the storyline that would have led them there naturally.