There is a demo now!

You don't really need the expansions, there are some that are kind of nice depending on your playstyle.  I bought the Islam one, and have yet to ever play an Islamic character.  For some reason, it doesn't interest me.  But, I play a bunch of Orthodox nations, so Legacy of Rome was a good one for me.  But if you just want to play a normal Catholic game, then you really don't need any of them.  

Kill children.  Killing children solves a lot of problems.  Or change the inheritance laws if you can.  Hopefully, if you planned ahead, you took over another conty in the same duchy as your own so now you can become a duke?  If not, you may have to do some murdering.

I hope it's in the same duchy, it's right next door... I'll have to look at the documentation and find out how to call myself a Duke - oh wait, what documentation?

Good to see that it's only $5 on Steam.  $10 for the other two though.  And so much DLC that I want to throw up.  That stuff should have been included in the game to start with, no?

They are groups of 500 soldiers that you hire. You can hire them = to the percent of your realms man power that you have in whatever tech tree it is. Different units have different costs, like archer - 1 point, H infantry - 2 point etc. They are always up and each culture has its own special retinue (Scotish Pikemen, Welsh Longbowmen, etc.)

Edit: You probably won't be able to get them anywhere near the start of the game unless you start as King, Emperor, or Something.

It is much funner to work your way up, but you will have to wait a bit to have any amount of manpower needed to field a retinue that way as it takes your and all your underlings levies into account.

My brother rebelled against me last night.  I captured him, and then blinded him.  He rebelled again, so I kept him in prison a few years and then castrated him.  I think he learned his lesson.  Might have to kill his children too.  

We have gavelkind as well, which meant that when my first character died, it split the realm into a vassal countess and a duchess.  Then, my character had a son! Woohoo, inheritance through males first!

So I thought, I should kill this countess and take back my land, being next in line.  Unfortunately, she passed away from illness before I had a chance to just knock her off.  So now I have Demense 2 again, and I'm starting to press my de jure claims against the rest of my duchy of Ulster, while still being squeaky clean.  Though, piety took a hit as there's a crusade going on.  How can I worry about that when there's so much to do locally?

My 500 troops would certainly turn the tide.  I am not in a position to kick butt.  I can't even start that war against England that I have a claim on, thanks to the Prince of England being married to me...

As for DLC prices...Steam puts them all on 75% sale several times a year, just wait for that (assuming you got it on Steam of course).

And as you can see many of the "baby" DLC are just art and music so you can skip them, no gameplay there.  However I pick them up when they are like 50 cents each on sale, what the heck.