I'm afraid I'm probably not really much use here as I started on Macs & only later tried to shift onto windows rather than the other way around. The thing I mostly find is how often I get surprised by things which I thought were very basic & easy, & had taken for granted as being that way, which are much harder to do on windows. & a lot of little fidly things that I am used to not thinking about... the OS would take care of them, but which you have to do manually on windows. But for the most part these are fiddly little things. I personally find windows to be clumsier, but in real terms there's not that much difference in using them. Just play with it a bit & it'll slot into place. Like mucks said. It's just like learning your way around a new car. The controls might be slightly differently arranged, but they still do much the same things
As for software, I run Microsoft Office for mac & have no trouble with it, but, unless all you want to do is write a letter (TextEdit can be a breath of fresh air after all the clutter in word but it won't handle anything complex) then you will need to get some version of Office. The eqivalent functions aren't covered by the OS itself.
I have found, with some software, that the mac version & the windows version of the same program do not always have all the same features or lay them out in the same ways so you may have to re-learn some supposedly familiar programs. Also, with paid software it is not uncommon for the Mac version to be pricier than the windows version. I'm afraid I can't see this as anything but a rip-off.
As a photographer you might like iphoto. I have found it much easier to use & more versatile than programs like Kodak or cannon. Although I am still using the Panther OS. I've never used the more recent versions & can't speak on them.
Myself I do use a two button mouse. never understood the big deal made about it myself
There are plenty of mice out there that are mac compatable, if you like a 2 button mouse then just buy one