There is also Customers Gallery and Google Analytics for free there ... but they're not that important.
From WP-Admin>Plugins>Add New (Search Box)
WP Super Cache
Open Graph for Facebook, Google+ and Twitter Card Tags (Ignore the Google+, it's been scrapped)
SMUSH (Image size reducer)
There's others you could use, but they are not "must have", like
WP Quiz (post links to quizzes on your site to bring traffic)
Enhanced Media Library (Makes categories for images to make it easier to manage them)
Then are are other ones that use shortcodes, but you'd have to make a child theme and edit theme files to use them.
I haven't used SMUSH for several months. I use EWWW now. (Trying and testing different plugins is an ongoing process)
But when I did use it, I had no problems with image imports being blocked. Everyone's setup is unique. There other factors, different settings etc involved. What gives problems for some, causes no problems for others.