* There's a "main.js", and a bunch of empty .coffee files that were presumably generated via a generator. Choose one frontend language and use it.
* Vendor libs should go in vendor/assets/javascripts. This codebase has assets/javascripts/vendor, and then random vendor libs that aren't even in that folder, they're just in "javascripts".
* The frontend code is going to quickly become jquery soup. There's no structure, all code executes on all pages.
* Very minor, but OS specific files should be omitted from git (like .DS_Store)
* Test coverage seems pretty low
* The secret token is public in the git repo (Why not use secrets.yml and keep it out of SCM to be safe?)
There are a myriad of other minor issues as well. It's a good idea for a project, and would help a lot of entrepreneurs out of done properly, but there are some glaring code quality issues here that worry me about the project as it grows.
You're also right about performance. Loading unnecessary stuff on a page is just going to slow everything down.
It's a great idea and also being a relatively new starter myself I can relate. Hopefully you can take all the feedback everyone is giving and make your project better!
* why use protected_attributes in an new Rails 4 project? I'm curious what motivated this decision.
* if you're destroying records, you'll want to look into using the :dependent option to has_many to make sure you clean things up. However, you may want to carefully consider where in the app "deletion" actually makes sense; anything that winds up in an accounting system probably shouldn't be deletable at all.
* get the tests running. The version on Github has a controller test for "ZusersController" which doesn't appear to exist in the application...
* a minor thing, but it'll drive future contributors crazy: hard tabs vs. soft tabs. Ruby code is usually two-space soft-tabs, but even if you don't agree with that at least be consistent. There are files on GH that are a riot of mixed tabs (configurations_controller.rb is a notable example) and nobody's got time for that.
I'm not the best at catching replies on HN, but ping me on Github (same username) if you want to discuss further.