I can't find Skyrim Mod Manager, and I cannot install OBMM because it requires Oblivion directory.

How can I extract BSA file?

There are a few dedicated applications on skyrimnexus that will do it; I suggest you search there for "BSA". I use BSAopt, which works reasonably well once you get used to its quirky interface.

It's not quirky, it's just a batch-processor.

In Oblivion I unpacked ALL the BSA to the data folder and just did all my mod work and played the game with all the files from there.

There have been threads debating if that is a good idea or not concerning unpacking all the BSA for the game to use instead of making the game open the BSAs on the fly.
But in my case I prefer unpacking all of the BSA to the data folder.

I want to do the same in Skyrim. So do I make a folder under DATA that is named the same name of the BSA and then unpack the files to that folder? I guess I am asking how I know WHAT to name the folders in the data folder so that the game will use the folders and not the BSA files.

How does archive invalidation work in skyrim? I am using a body/face mod that replaces a texture files but it seems to work with NO extra archive invalidation steps as was needed in Oblivion. Will Skyrim do this automatically now?

There is no Skyrim Mod Manager. It doesn't exist. You can create a dummy Oblivion directory and it will work. If it says no Oblivion exe is found, create a dummy exe by renaming a text file to the proper exe name.

You should already have a Data folder, and the BSAs should be in it. A proper extractor should preserve their directory structure, so all you have to do is extract them to the Data folder and everything will line up.

Yes. Another change is that the Skyrim Launcher automatically activates every plugin in the data folder. You no longer need to activate the plugins manually, but you can't leave any test-esps in the data folder when you use the vanilla launcher to start the game.

In my experience... the Launcher is not really 100% consistent about checking new esp's. It's really confusing.

The default launcher is buggy indeed, mods that were checked in Wrye Bash weren't checked in Data Files. The mods worked, so as usual I have more faith in Bash than in the official data file handler.

EDIT: Now for something on topic: http://sites.google.com/site/ronsworkspace/GameUtilities/fallout3 works great for extracting Skyrim's BSA's!

I already have FOMM installed with FO3 so I just used that.