What we do is as soon as the user shows interest in the subscription (i.e. clicks the relevant link), there is a redirection towards PayPal where a recurring subscription is initiated after the whole transaction is processed.
Paypal then takes care of the rest. Its API reports back to the software and if someone's card is declined or anything like that, their subscription status changes. This way we do not worry about the subscriptions themselves.
Several things to note:
1. The software handling this comes within the software we use. Integration then is something that others have done and we do not worry about this. 2. Refunds are processed manually 3. Increase in the subscription price is a pain since the old users (the ones that paid with the old price) will continue to get charged the old price using this model. The recurring transaction from PayPal does not account for increases in prices. Therefore you will need to cancel those subscriptions manually and let the users resubscribe.
Customers are never emailed but everyone is well aware that these charges are taking place. We also use eSupport from Kayako which solves a lot of problems in customer support (you will need something like that if your volume is going to be high).
From another company that I had, we were using the ModernBill software. It handled a lot of payment processors and it was emailing customers. The processing was automatic on that one so in your case I would be inclined to use this piece of software.
I hope the above helps.