Can I use the Sites folder for whatever I want?

Not realizing that OS X creates a ~/Sites folder when you enable web sharing, I started putting my sites for MAMP within a ~/Sites directory, which did not exist on my new laptop. Is this ok, as long as I don't enable web sharing? Even if I did enable it, would something happen to the other files I put in there?

It's fine, just realize the built in apache server will share the files you have placed there unless you change the apple supplied httpd.conf should you start up web sharing.

Any files you put in the ~/Sites folder will be treated the same way most web hosts treat the files. HTML, images & scripts (scripts may need special changes to htaccess & httpd.conf) will be served normally from http://my-Mac-name-here.local/~jjeaton/ .

So, like a typical webserver, whatever files you put in there will not be changed unless you youself edit/move/delete them.

You should also double check the permissions so that only you have read/write/execute permission and group & others only have read/execute.