Okay, Earth Elemental + Meld into stone + familiar, is it viable? 

I agree.  Still useful to get into the position you want without opportunity attacks from other enemies, but once engaged it would cost you opportunity attacks to leave.  

In dnd you CAN have a living pet rock

I assume the elemental understands you based on the connection you have with it through the spell.  When concentration ends so does that connection therefore you would no longer have the ability to communicate with it, unless you speak Primordial: Terran, although it would still be aggressive towards you since you lost concentration.

At least that is how I would explain it running the game there might be other sources or GM's who have a different explanation.  

Quote from WanderPhil >>

I assume the elemental understands you based on the connection you have with it through the spell.  When concentration ends so does that connection therefore you would no longer have the ability to communicate with it, unless you speak Primordial: Terran, although it would still be aggressive towards you since you lost concentration.

At least that is how I would explain it running the game there might be other sources or GM's who have a different explanation.  

 i can see that

dont think so

Can an Earth Elemental Change shape, or is it stuck in one shape? I am wondering if I can somehow manipulate the stone of my elemental body while in wild shape?

Quote from Okashido >>

Is the burrowing speed and the earth glide feature the same thing? Like, does it have a burrowing speed because of the earth glide feature, or does it have the burrowing speed and the earth glide ability?

 technically it just burrows through the earth like it was liquid or whatever it says. it has burrowing speed and the ability to earth glide so it justs earth glides.

Can a Wizard use his conjured Earth Elemental to help in the construction of his tower? 

Mixed with some Stone Shape and Mending, seems like the easy way to go.  This assumes you're not able to cast Move earth yet...

no

Are elementals immune to sneak attacks?

No, why would they be?

How tall is one of these cuz large is 10 feet but I feel like it would be 8 feet for some reason

Quote from marshmallow_castle >>

How tall is one of these cuz large is 10 feet but I feel like it would be 8 feet for some reason

 The "Large" size only represents the size of the area that the creature threatens, it doesn't necessarily mean it's actual height.

Quote from Lomonocrat >>

If they only speak Terran, how will an Earth Elemental understand my half-orc's verbal commands when I summon one with Conjure Elemental?

 The Conjure Elemental spell says, "The elemental is friendly to you and your companions for the duration. Roll initiative for the elemental, which has its own turns. It obeys any verbal commands that you issue to it (no action required by you). If you don't issue any commands to the elemental, it defends itself from hostile creatures but otherwise takes no actions."

So the spell would seem to give it the ability to understand your commands.

Terran is a dialect of Primordial. If you can speak Primordial you can understand it

Why did they drop the size variable of elementals. Now there is only a large elemental.

Quote from Krisancia >>

can an earth elemental be diseased?

 

 

Beyond 20

 

 

 

 

 

 don't see why not, probably would be magical diseases though