Optiplex 755 information

I have another item I am looking into. I know all my posts have been for older computers, I am buying them from work - so they will be a few years old and usually be business not gaming machines... This one is a Optiplex 755. I am curious as to a couple things.

The tag line for this model is - 

DELL COMPUTER OPTIPLEX 755 2.00GHZ DUAL CORE DTP 80GB 2048MB

which means it is a Dell Optiplex 755, with a 2.00 ghz dual core cpu (probably a E2180 from previous experience), DTP should mean the DT or Desktop model, the 80gb is the hard drive size and the 2048mb is the amount of installed ram it comes with. I realize that I will need to bump up the ram and increase the hard drive size over time, but my more immediate needs are going to be a video card and a new CPU. I am thinking I will end up with an E6850 cpu since it does not seem to support the E7400 I was going to go with (using it on an inspiron 530 desktop instead for my wife). My main concern is...

1. Will this computer use a standard pci-express video card or is it going to need a half height card using an adapter?
2. Will it run high density ram? I did some research and there is a lot of misinformation out there about how only AMD computers can use it or only 9-10% of computers can... I am curious if anyone has tried on this particular model an gotten it to work.
3. I would like to get input from other people that use the Optiplex 755 and get some input on what they recommend upgrading on the system to make it more of a personal computer than a business machine.