I do not recommend buying your shoes before your gown, as colour matching is easier once you have chosen your gown. Most retailers/designers will have colour swatches you can borrow to match up against potential shoes.
It is important to be fairly sure what height heels you would like to wear on your wedding day as you prepare to go in search of your gown.
Even though your final fitting will be a lot closer to your wedding, most designers have standard length or petite length gowns. In addition most designers allow an option of adding extra length to your order. So having the correct height shoes is very important when placing your order.
If you are planning to wear a hoop under your gown you need to be conscious that the hoop will push the hem out and upand is therefore important when choosing the correct gown to order.
Quick tips;
You will be wearing your shoes for an extended length of time so make sure the shoes you buy are reasonably comfortable. Some bridal shoes have special padded inserts to promote comfort.
Wear your shoes in. Spend some time walking and dancing around the house!
UNDERWEAR
I do not recommend buying your underwear until your gown has arrived and you can see exactly where all the lines run and then purchase underwear that will not show over these lines
There is an extensive array of bridal underwear available and plenty of choice whether you want to go all out with the basque and stockings or tone it down and go for bra and pants.
Always have a back up set of underwear on your wedding day. It may be that on the day the underwear you have chosen just doesn't feel right, it keeps slipping down for instance or it's too hot etc.