Hey Rallaster! Here are some thoughts, some certain and some tentative.
You mention that both of you have $0 currently on all your credit cards. This is definitely hurting your scores. It looks to FICO as though you don't know how to manage credit card debt. You will both quickly gain a fair number of points by each resolving to use one card at least once a month. All you need to do is show a small positive balance on your statement. Then after the statement prints, pay the amount in full. It can be small amount if you like and it only has to be on one card.
As far as unsecured personal loans, there is no low-interest option that I know of. That's what happens when you ask a bank to give you cash but don't give it any collateral. There's a much greater risk that you could walk away with the money. So they always charge much higher interest than for (say) a car loan or a home loan, where the bank can take the car or home if you default.
The one exception to what I described are lenders who specialize in giving lower interest unsecured personal loans, but they typically only give these best rates to clients with ultra ULTRA high credit scores. E.g. at least 780. Yours are 745. Lightstream is an example of such a lender.
How long are you guessing it would take you to pay off the cost of the wedding? If you think you could do it in a year, your best option (given your competing desires) might be to apply for a credit card that gives you a 0% introductory rate for 12 or even 18 months -- and use that card for the wedding. Before you do that, however, I would wait until you have one CC reporting a positive balance to the credit bureaus, which will raise your scores significantly and make you more attractive to the CC issuer from which you hope to get the 0% offer.
