If I am wrong I will make a huge public apology.
Russia has a bunch more ports on Black Sea. However Sevastopol is an old, established base of Black Sea Fleet, with several convenient bays with controlled access. Compare to Novorossiysk that is open to the world and is not very good as a military base.
and is not going any further.
It is quite possible that more Ukrainian territories will want to join Russia. Maybe not today, but in a year or two, when the favorable economic conditions (that will be provided to Crimea) become very, very attractive. Today, though, the public opinion in Eastern Ukraine is not yet ready to join Russia, and no moves will be made to that end.
But regardless of what provinces are affected, it will be all done through a public vote, like today's referendum in Crimea. It will be perfectly democratic, and nobody will be able to object to that. Well, some do, but what kind of selective democracy do they preach? Don't the people have freedom of association? They are not slaves of Kievan boyars, you know...
I agree that Crimea is likely as far as Putin will go...this round. However with the condition Ukraine must meet, to allow US missile sites on their land...if they move on that Putin may well then move on Southern and EAstern Ukraine.