non-mikrotik stuff you need:
radius server = platform for authorization into your wifi access point as well as accounting so you can kick users off after x limit or charge extra etc, look up userman if you want something lite that is run on the mikrotik as well or look up something like free radius.
payment portal = ? not sure for this one, I know there is a heap to do with paypal + mikrotiks but I have not personally used this payment method (I use freeradius)
Mikrotik stuff:
hotspot service = need this so that you can authenticate individual users as well as this will help with accounting etc.
radius client = hooks the router up to the server(still needs to be done if your hosting userman locally on the device), tells the router where to send authentication and update requests as well as lets it choose if it will listen to incoming messages from the radius server
Limitations
Dont think self sign on works well with userman to be honest but again there is some information out there regarding it, I personally would jump over to freeradius at that point at it will open up a lot more configuration for you.
It sounds like you are just starting off with the mikrotiks so I would suggest looking at setting up a router that is able to access the internet through the hotspot service first then look into the radius stuff from there