Questions about switching from PC to Mac

[gerich]

I'm seriously considering switching from a PC to a Mac, hopefully the 27" iMac. I currently use LR5 and PS CS6. From what I've read LR is multi platform and I can apply to Adobe to switch PS to the Mac platform. I know my newer USB powered EHD's are compatible though some of my older EHD's may not be and I'll need to juggle data to be able to reformat them.

So my question is, is there anything else I should be aware of before I make the switch? ie commonly used hardware or software that may no longer be useable, is virus protection necessary etc? Just want to educate myself on what to expect cost wise other then the actual iMac.
Also for those who are on Mac, what would be the minimum processor, RAM, graphics card etc that you would recommend to comfortably run both LR & PS at the same time? I'm happy to upgrade specs but I don't want to be over the top about it. Thanks in advance for any help.