Is Multisite the RIGHT option for my case?

There is really no answer given the limited facts in the question. Are you requiring that users login to see pages/data? If not I don’t see why you would care to share user tables. There will be some things that multisite will handle better but there will be some things (handling certain plugins) that multisite will make you pull your hair out.

If I had two sites on the same domain for totally different purposes (functional vs. blog) I would have two separate installs of WP. Just because I have gone through the one off issues of multisite and the time it saves is not worth the time you will put in for one more small site.

Also if I had a functional site and a blog that would just be one wordpress install. I run sites that have 4-5 different functions plus blog with no issues. I am not sure why you need different install for this. You just need to create some custom post types to hand the functionality of the site and use regular posts/pages for your blog.