yes the E-ATX states the form factor of the motherboard.
and what to look after when you are getting a case.
menny cases can fit several types of sizes boards.
example ->
http://www.newegg.com/Product/Product.aspx?Item=N82E16811129224 <- this supports Micro ATX / ATX / Mini ITX / E-ATX / XL-ATX motherboard sizes.
and this is a full tower case
example ->
http://www.newegg.com/Product/Product.aspx?Item=N82E16811119260 <- this supports Micro ATX / ATX / Extended ATX ( full tower case )
example ->
http://www.newegg.com/Product/Product.aspx?Item=N82E16811139038&ignorebbr=1 <- this supports Micro ATX / ATX / Mini-ITX and is a ATX mid-tower case
so as you can see there are cases to pick from but you have to look at the form factor of your motherboard and on what form factor the cases supports.
http://www.newegg.com/Computer-Cases/Category/ID-9there are cases that have PSU instaled and there are those who dont have it instaled ( including in the price ).
and yes there will be a bit hot in there if the GPU's are going to be on full load over time ( 1-2+ hours ) so thats why i recommended a case whit good air flow in my last post.
for custom water cooling you will void warranty if you start to take off the stock coolers on the GPU's ( just to have stated it ).
now HERE you will see things will start to cost.
for each OC'd component you will need 2 fan slot's of radiator surface to cool the component.
you will need the case for it ( for example the 900D you was thinking of )
you will need radiators.
you need blocks for all the components you are going to cool ( CPU + GPU blocks ).
you will need a pump and a reservoar to fill the coolant in.
you need tubings.
you need fans.
you need fittings.
you need a drain point on the lowest point in your loop.
i would recommend a good fan controller.
i would recommend temp probes in the waterloop to monitor the water temp.
you will have to change the coolant once a year.
if i was going to guess the price? i would guess up to $1000 for it all, thats just a estimate guess, it can cost more or less then the amount i posted.