Can you use the Logitech Wireless Solar Keyboard K750 and the Apple iMac Screen, by only buying the screen/monitor, but connecting this keyboard

I recommend buying the machine with a wired Apple keyboard regardless, as some system diagnostics are only possible with one. As long as the Logitech either has Mac drivers written for 10.7.3, or no drivers at all and is either bluetooth or USB ready, it should work with the iMac. Note, if there are no Mac like keys on the keyboard, your Alt key acts as your Option key, and your Windows key as your command key unless the drivers switch them. A few keyboards I found are not Mac compatible without Windows installed, such as the iHome by iHomecomputer. Double check with Logitech what their keyboard's compatibility is.