I’m no EE expert myself, in fact I’m a rank newbie. But I’m no newcomer to web design, and from a purely “best-practice” standpoint, I would strongly recommend against installing a second platform when your existing one will do what you want with proper setup.
There are at least two major reasons for this:
1.) You’ll be adding an extra layer of complexity to your site (extra login, extra templating system, etc.)
2.) You’ll be adding another potential attack vector for your site (and, in the case of WordPress, a very commonly-used attack vector.)
Basically, risks go up and ease of site-management goes WAY down when you begin mixing systems like this.
I highly recommend finding out how to set up a blog in EE and do it that way. It may take longer, but better to spend a little extra time in development than a LOT of extra time in the weeks, months, and hopefully years ahead, which is what will happen if you divide your site into multiple platforms like that.
Just my perspective, hopefully someone else will chime in as well. 😊