A good thing about Evernote is that there is a huge amount of information out there about it.
A bad thing about Evernote is the information is spread all over the place, which can make for a lot of searching around if you want to find something.
A page I refer to all the time has been put together by Christopher Mayo, an associate professor at Kōgakkan University in Japan (and an extremely helpful member of the Evernote forums).
Christopher has compiled together all the limits that exist for pretty much every area of Evernote on almost every platform in his monster list: What Limits Exist for an Evernote Account?.
Below are some of the limits that I know about for Evernote accounts. For limits that I am only guessing about, and have not seen in writing, there are no links.
If you want to know what the differences between the Free account, the Premium account, and the Business account are, Christopher’s list is the place to look for Evernote account limits.
Every time I visit his site, I learn something new. For example – I had no idea there was a 100,000 limit on tags. Good to know. The way some people tag things they’d better watch out.