Set Up OpenVPN, similar to Astrill/VPNinja

[md50]

Sorry if this is in the wrong section. I don't see the "questions BEFORE using" forum.

I'm looking to run a similar service to Astrill or VPNinja. Both of these are rather popular here, but both are really looked at by the Chinese Gov't. What I was thinking is not a service that has 10,000's of users but maybe a mere 100-200.

I like how you can log into any device with Astrill, although you can only have one online at a time.
VPNinja allows 2 connections, but are limited to those two devices.

If I can combine that, i.e. only 2 devices online at once, but also not limited to 2 specific devices, I reckon I could convince a few people to sign up. I'm hoping to have the service pay for itself only, or making enough money to allow a 2nd server in another country (US First Choice, possibly UK server 2nd choice).

This means I would have users. I've never even SEEN the back end of OpenVPN so I don't know how it would handle users (year at a time accounts, half-year, whatnot). Is this built into openVPN by default, or do I need a 2nd program as well?

I'd also need some sort of downloadable log-in. Again, no idea if this even comes with OpenVPN. Is this part of the program, or do I again need a 3rd party program?