If you are interested in Bitcoin mining, the HD7990 is the only viable card of those three for that purpose. Otherwise, at least until possible driver fixes in July, FCAT testing has shown that Crossfire is [badly] broken, whereas SLI is not. SLI does not scale in every game though, so I would probably choose the Titan. For single monitor gaming, however, the cards I would suggest you consider are the HD7970 and the GTX670. Both are much cheaper than your selections. Once again, if you're also interested in Bitcoin mining, the HD7970 is the only rational choice of those two.
Without knowing what specific models are available, I can only offer general suggestions. I prefer Asus and ASRock motherboards, but Gigabyte is also good. I would avoid MSI, especially if you're interested in overclocking.
Using only SSDs will make your system very responsive, but will not improve FPS in games, and is expensive. My own preferred configuration is a single SSD system drive, then a pair of mechanical HDDs in RAID1 (mirroring) for data.
For the monitor, I prefer my 21.5" LED monitor to my 23" conventional-backlight LCD. Both are 1920x1080.