put it all in a database on your server run a cron job (ie, php script that runs automatically same time every day) to send emails with payment instructions do the same for anything that requires regular payments
check modernbill - it's for hosting, but don't know how well it'll automate things for you
I just set the hosting date in Outlook as a yearly recurring appointment. Set it with a 4 week reminder and send the invoice when the reminder goes off. Works ok for me, but of course if you don't use Outlook then a simple spreadsheet/text file listing each client and their renewal date is a good alternaitve. You need to get into the habit of checking the file at least once a week tho!