Default rails apps come setup for the SQLite database but SQLite is not supported by Heroku. You may want to use Postgres initially instead. https://www.digitalocean.com/community/tutorials/how-to-setup-ruby-on-rails-with-postgres
Devise - gives you "all the things" - you use omniauth to setup social media login, allow password resets, setup email confirmation, register accounts. https://github.com/plataformatec/devise
Pundit - you can create your own authorization system to create user roles and page access or use something like pundit. https://github.com/elabs/pundit
Bootstrap - use the official gem. The others are junk. https://github.com/twbs/bootstrap-sass
For charging credit cards but f you need an e-commerce store, just setup something like Shopify or Big Cartel. Don't build one by hand with Stripe. https://stripe.com/
If you need to do bank transfers directly from someone's checking account. https://www.dwolla.com/
For sending automated text messages to people. https://www.twilio.com/docs/
For deploying your Rails applications publicly to the internet. They have great documentation. https://devcenter.heroku.com/articles/getting-started-with-rails5
You can find about setting up your website name here on Heroku. https://devcenter.heroku.com/articles/custom-domains
You have a ton of choices here. Here's a good post on picking which one is right for your app.
- Amazon SES - https://aws.amazon.com/ses/
- SendGrid - https://sendgrid.com/
- Mandrill - https://mandrill.com/
- MailGun - https://www.mailgun.com/
- Postmark - https://postmarkapp.com/