Happily, figuring out what tech we'd use was a very very small part of the ForceRank build out. We'd both used Rails in a previous life and our return to the fold was smooth sailing. Things have only improved since we left.
TurboLinks is fabulous. Not seeing the page flicker everytime you click a link just feels fantastic. I don't have numbers to prove that this has helped us, but every study ever done says that perceived website performance is the most important thing and I think this really helps us.
Look at me not writing ANY authentication/user-management code because Devise just works.
Look at me styling a responsive site even though I am garbage at CSS because Foundation is fabulous.
Look at Stripe just being the most mind-blowingly developer friendly service you can use.
Look at better_errors just being embarassingly useful.
Look at letter_opener solving a problem I remember spending tons of time on in an earlier life.
Oh and Heroku. Yeah. So good.
As far as Heroku addons are concerned, HelpScout in particular seems to have fit the bill. Just seems to work. We tried Intercom and MixPanel, but you get into pricing tiers that are unaffordable very quickly.
Anyway have a peek a the Gemfile. Consider bucking the trend and not building an enormous single page app. If you're trying to solve a user's problem this basic Rails stack is the right answer for many many things.