Is it possible to get more aetherium to make all three aetherium items. If not which item did you make?

Nope just enough for 1 item.

I believe not, it's nice actually making a choice that matters once in a while playing Skyrim.

Anyways, the crown and shield are really epic, but you gotta make a tough choice which one you want.

The summoning rode or whatever I just think isn't as good as the other two choices.

I went for the crown. Having two standing stone powers at once is pretty handy, and it does look really cool. I didn't really want the shield that much and the rod seemed kinda useless compared to the other two.
I ran into a dark elf who asked me where i got the crown from but i was a werewolf when he asked me.. so you can probably guess where that conversation ended up.

for the crown do you only get the power of two standing stones when your wearing it.

yes

I chose the shield because it looks amazing, i think its the most beautiful shield in the game. Plus the crown would mess with my heavy armor effects so i would lose alot of armor rating if i wore the crown.

Not necessarily, and is worth some personal testing.
I currently have the crown in my inventory, not equipped, and the two chosen stones are shown as active on my Active page.

1. Initially it would remove the previous stone when unequipped and the Active page would reflect this.
2. So I unequipped the crown, chose a third unwanted stone, then went and chose what would be my secondary stone.
3. I then travelled to my primary stone, chose the stone, then equipped the crown.
4. After unequipping the crown, both my desired primary/secondary stones remain active.

We don't yet clearly know if you need the crown equipped or just to choose your stones.
Whether glitch or intended gameplay, my current Dawnguard character has two active Standing Stones and is wearing a helm, not the crown.

Time will tell but, for now, perhaps you can try the above steps for yourself and see what happens.
Hope that helps