If you've ported in your number from O2, your original Smarty number has now gone. It will eventually be reallocated to someone else when they join Smarty or Three. No, you can't have both it and the number you ported in.
There is no bill from Smarty, it's a prepay service, so each month you are paying in advance for a package of data, minutes and texts. As long as you have auto renew switched on, the payment will be taken automatically from your registered payment method each month.
Your O2 SIM should go dead at some point on the day of your number port. You can throw it in the bin once that's happened.
