Do you think Windows Defender is enough to keep me safe on my PC? Does Windows have anything similar to OS X's System Integrity Protection?
I don't know much about OSX, I read about system integrity protection, but that doesn't sound like the greatest feature. it's taking your freedom as I read it, because even people with Sudo can't have full freedom.
One thing you have to remember it's that Windows security is not only about anti-virus/malware it also comes with Smart Screen on Edge/IE and Store apps, so if you download something and it's suspicious or reported as dangerous, it will give you the message that it couldn't download it.
Also there are some places on Windows where you can only modify them by going into adv permission and change the owner, the permissions... you know, they can't be modified but they need a big of extra work.
some application elements also go to VirtualStore on your local folder on your profile, and that means those apps didn't have admin rights and wanted to write elements to their folders.
In theory you shouldn't run anything but installs as admin mode, so if a strange program you download asks admin permissions, you should say no. that's the common sense I talked about on my first post. Defender is okay, it misses some important features other antivirus have, but sometimes the other extra features seem to bring high false positive alerts.
There was a report few days ago that showed Defender getting better on ranking, maybe that's made because of the cloud protection they seem to have added on windows 10.
You can easily get free and paid antivirus, but few ones seem to add to many things. you could also download sandboxie or BufferZone Pro or something like that, which add extra layer to run programs that are probably suspicious, but you still want to run them but you want to be sure they don't modify anything on windows.
You could even get Eset AV or security essential and find leaked keys around internet. there are many ways of adding extra protection, I don't use them.
you could also use Jotti or virustotal if you want to know results on other antivirus. maybe Malwarebytes and check files manually, it's rare to see people using the realtime feature on the pro, people usually use it to check files manually.
so as you see anything on windows shouldn't be less safe than OSX, of course there are more virus and malware on internet targeted to windows, but in recent years, it has been less of a problem.
Just never run anything truly suspicious and you will be okay, Defender might catch it anyway.