I use Broken Link Checker
>Unfortunately any link checker can put a lot of strain on your WordPress database and slow down your site, all depending on your server setup. (256mb+ memory should do, I have had no problems) That’s why you should use it and turn it off/de-install it afterwards. And do not use it at prime time!
But starting about plugins; yoast for seo is a must; and Wordfence is a nice basis for better security.
I am also a fan of bullet proof security; a .htaccess security solution.
These can be combined but do require some knowledge/time to learn what they do.
This should keep you busy for a day or so. 😉
Again if I can help let me know. (not promoting any plugin/my own services!)
Gladly would help you with this; this is my expertise; just let me know!