Get the extensions, they will look great, doesnt matter how bitten the nails are, they can do it, dont go for extra long ones as you wont be able to cope, the most natural ones are normal size and a "french manicure" looks good on first timers- thata where they paint a white line across the top.
But if you want to go real fancy, take the wedding outfit top or skirt with you and get them to match up the colour for your nails and have air brush design on them. loads to look at and choose if you go to one of the new nail shops where the Vietnamese work and their work is far superior to the British nail salons I have to admit, also for sheer luxury have your toe nails painted just in the plain colour you chose, costs more but its a once off wedding, then if you wear open strap sandals you will look real good.
Only have the work done one week before the wedding, later than that if possible, your own nails do grow underneath and after three weeks you will have to decide whether to go for an infill or take them off.
I have been having mine done for years otherwise I love a good chew at my nails.
Good luck and enjoy the wedding, you wont be sorry you got them done when people start complimenting you.