From what I have found in Scripture, Heaven is a real place with events happening, and is populated.
For example, we know the angels are there, and that a certain type of angel surrounds God, and His Throne.
We will not live in heaven for eternity, but on the new earth, but we will be in heaven for the 1,000 years, while satan and his angels are here alone.
After all is said and done we could say it will be heaven on earth
Now regarding no sea etc.. I am wondering since the new earth will be like How Eden was, wouldn't it make sense that there be an ocean? I like to think of God not only as My Father, and Creator who sent His only Son to take away my sins, but He's an artist.. The ocean and its creatures are the opposite of the air, and its creatures i.e. flying fish\Butterflies, deep oceans and valleys\Air and Mountains.. Its really amazing, or maybe I have watched too much of BBC's Planet Earth
We only have nuggets of information how it will really be though, but we can be sure it will be something like we have never seen, imagined or heard.
God Bless,
-Will