Serial entrepreneur, developer, geek and ski fanatic! Former CEO of privateproperty.co.za, co-founder of WeThinkCode_. Love startups and helping people succeed.
In the short term I think you will get going quicker with Wordpress with some plugins that should enable what you are looking for.
But to make this decision I would first consider if this version of the product you are looking to build is just to test if your business can work - like an MVP (Minimum Viable Product) - or is it the long term version of something already tested and proven.
If you are still trying to figure out if what you want to do has any legs, then I would go with wordpress. Get it running in a few days and test everything you need to make it work. For example getting users, creating the content you need and learning how to convert visitor to paying members. If you spend a few week/months on this and you get answers to all the non-technical questions, you can also re-asses if it is time to build a fully custom solution.
If all the other parts are already figures out and you want a custom build technical solution that allows greater flexibility I would use Rails. Or some of the other frameworks like node.js or CakePHP.
There are also some software services online build for this. So make sure you look at them as well.
The beginning is always the biggest challenge for me, you have to hussle in the short term to get things going.
You say that the service has huge value, but have you tested this with users to make sure their understanding and perceived value of your value proposition is in line with your own?
I have recently read a few books that you might find useful.
1) Ask - Ryan Levesque
2) Inbound Marketing - Brian Halligan, Dharmesh Shah
You can also find loads of information about inbound marketing online.