If you receive gifts before the wedding is it ok to send thank yous at that time, or should you wait until after the ceremony (and then thank them for attending etc.)?

Yes, you can certainly send thank you notes for gifts received before the wedding as you receive them. You should send them no later than 2 weeks after receiving gifts before the wedding date. Since you will probably verbally thank everyone for coming at the reception, you need not send them another thank you note after the wedding. One thank you note per gift is enough. Gifts received at the wedding should get thank you notes within a month of your honeymoon return and within a month if it is received afterwards.