It's kind of a lot, but there are some important jobs that have to be done on a lead-generation site:

• https://wordpress.org/plugins/broken-link-checker/ Because broken links suck. (Edit: my WordPress expert buddies tell me to disable this except when needed because it breaks stuff.)
• https://wordpress.org/plugins/404page/ lets me create a custom 404 error page with valuable resources and a list opt-in instead of a generic 404 page
• https://wordpress.org/plugins/duplicate-post/ lets me easily duplicate pages (and blog posts, but I only use this to dupe pages) without jumping through the typical WordPress hoops
• https://wordpress.org/plugins/email-marketing/ Adds the Drip JavaScript code to the site for me.
• https://wordpress.org/plugins/wonderm00ns-simple-facebook-open-graph-tags:/ to put Opengraph tags: on posts to enhance social sharing results.
• http://www.gravityforms.com/ middle price tier option for easily adding contact forms and opt-in forms.
• https://wordpress.org/plugins/drip-gravity-forms/ Lets me hook up Gravity Forms to Drip and bypass Drip double opt-in as desired.
• https://wordpress.org/plugins/gravity-forms-no-captcha-recaptcha/ adds the least awful Capcha I’ve found to Gravity Forms.
• https://wordpress.org/plugins/header-and-footer-scripts/ To let me add custom script to header or footer. Rarely needed since I've migrated away from LeadPages and started using GeneratePress premium.
• https://managewp.com/ for backups and maintenance.
• https://wordpress.org/plugins/quick-pagepost-redirect-plugin/ for page redirects as necessary.
• Thrive Leads for rapidly building opt-in forms and AB testing.
• https://wordpress.org/plugins/dvk-social-sharing/ My GAWD are most social sharing plugins overbearing and ugly! This one fits my preference for creating simple text social sharing links.
• https://wordpress.org/plugins/wordpress-seo/ for SEO tweaking (I don’t do much, just manual page title and descriptions)
• https://wordpress.org/plugins/postmark-approved-wordpress-plugin/ for handling outbound SMTP mail from the site, which tends to be way more reliable than letting the hosting provider do this.
• https://wordpress.org/plugins/shortcoder/ for creating re-usable text, HTML, or code snippets.
• https://wordpress.org/plugins/open-external-links-in-a-new-window/ makes it so external links open in a new window without manually checking the "open in external window" checkbox, which I prefer. You can build an exception list to exclude certain domains from this behavior.

I use the GeneratePress theme, Beaver Builder, and Thrive Theme's landing page builder. All three play well together and give me all the flexibility I need to crank out pretty much any kind of regular page (I just use a regular theme-styled page), sales page (I tend to use Beaver Builder layouts for these), or landing page (Thrive's landing page builder is nice for these).