I am building a SaaS web app on Ruby on Rails. Is there a relatively simple way to integrate it so that I can manage my customers with openerp (and avoid building my own crm and billing system)?

What about integration to a payment gateway/account for accepting credit card payment, eg braintree/stripe?

Without openerp I would manage subscription payments and credit card processing with something like braintree or stripe and import transactions into an accounting program manually.

My professional background is as a SAP consultant and would love to use an ERP for my small tech startup company, but don't want to make a huge investments in infrastructure at this point.

Cheers, Fraser