What is the process for signing up to UO?

I've got myself another copy of UO from Ebay. This one is Samurai
Empire. I have a few questions about it.

I signed up with EA about a month ago for a free account ... now it
doesn't recognize me ... I suppose I have to sign up again? Do I really
need to register with EA?

Does the fact I have the Samurai Empire add-on allow me to play in the
Britannia portion of the game or not? I assume these are different game
worlds and you can't go from one to another?

I downloaded the Mondain's Legacy 700Mb file from UO. Do I actually
need to install SE or can I use my product code to install the ML file I
have?

Also my understanding is that I join a shard which in computer terms is
a particular UO dedicated server which may be free or ask for payment.
I pay the shard organizers and not EA ... is that correct?

Do the shard organizers pay a license fee to EA to use their server
software? Or do EA actually own the shards and get the money directly?

I'd just like to know before I start spending money on things that I may
or may not need.

As ever ... thanks in advance.

Bill
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Bill Jillians