Does this scrip support auto suspend after x days of non payment? If not how hard would it be to mod it to have that feature?
yes, it supports autosuspend.
Suspended acc will show u the reason in whm as "5 out of 15 posts completed" or something like that.
you can edit the suspension time etc in admin panel
Yep, it does. Just make sure that you set up the cron job.