I started with Windows and switched to Mac at the suggestion of my roommate at the time who was a PC programmer-- "You're a photographer. You need Mac." Simple as that.
Ten years go, Microsoft Office was not great when sharing documents between Windows and Mac OS. Nowadays, it is 99.99% faultless. Any Word doc created in OS X Word is fine in Windows Word. I share such documents with my students all the time, no complaints, no questions.
You have several options in office software...
-- MS Office for Mac. Does everything the Windows version does, costs a pretty penny.
-- Pages / Keynote / Numbers, each costs $19.99 at the App Store. All can open old-style .DOC /.XLS /.PPT fine, edit, save fine. Can open new-stye .DOCX, .XLSX, .PPTX ("OpenOffice XML") files, but can only save them as old style. Keynote has way better transitions than PowerPoint (MS has copied most of the Keynote '06 transitions to try to catch up), but cannot apply more than one song to groups of slides like PowerPoint can.
-- NeoOffice / LibreOffice / OpenOffice can open and save all Office docs, old or new style. NeoOffice version 3.1.2 was free, still works with latest Mac OS, but no longer on the official site. Newer 3.2.1 version is ten bucks. Libre/OpenOffice are free, but rougher to use than Neo-- poor highlighting, no central menu bar.
In general, easier to do keyboard commands in OS X. See link below about screen shots.
Windows has no "central" menu bar at the top. All documents have their own menu bar attached. Two considerations: Screen real estate lost to five menu bars if you have five documents open. Also, close all documents in Windows, the app must quit itself. In OS X, an app doesn't care if you have documents open or not, it keeps on. You have to decide to quit. Creative folks love this, because they can close all documents quickly to work in another app, and come back minutes later to use Photoshop again without launching Photoshop-- it was not quit, so it is just waiting in the background.
Saves time in the publishing--advertising biz where loading a menu of 500 fonts will slow opening Word or PS again.
Some commands are obviously like Windows, but command instead of CTRL: Command A selects all, command C to copy, command V to paste, command N new doc, command W closes the window--oops, not exacly like Windows.
Theming is extremely difficult in OS X, so I suggest do a lot opf research or forget about it.
BEST THINGS: No BIOS, no registry.
About external drives:
Format "Mac OS Extended" to use drive with OS X only.
or...
Buy "Paragon NTFS For Mac", install it, format the drive NTFS for use with both OS X and Windows (share with a PC).
or...
Buy "Paragon HFS+ For Windows", install it in Windows to use any Mac drive with Windows.
Apple's Time Machine backup only works with "Mac OS Extended".
or..
Partiton the drive, format one partition Mac, other NTFS.
but...
Do not format any large drive FAT-32. FAT format is for small drive volumes. It is a bad format to use with large drives-- kills efficiency.