Yes, yes, and a wedding is not a good time to be wearing thin, high heels if you’re not used to them. I assume that one is.
Antiques are so very hard to tell with - there’s no single answer I can give you. The best advice I can give is to check with the estate sale organizers, ask if you can inspect the dress before the auction. If they say yes, then you want to bring a pair of thin white cotton gloves with you (so you don’t get skin oils on the dress).
Check for the following in order:
Try to fold a section of the fabric. If it breaks where the fold is - No Good. If it feels “crunchy”, or is difficult to bend - No Good.
Look at the fabric in different areas. Check for yellow under the arms and around the collar (from sweat). Check for browning in areas with distinct linear borders(from where it has been folded and the top fold exposed to the sun). Check for rust spots at the waist, around any fasteners, and at the back where bustling may have happened with pins. Check if the beading or lacework has discolored from age in a way that doesn’t match the material of the dress. None of that can be easily repaired - better to just say no at the start.
Look closely at beading or lacework - most often there will be parts damaged or missing. That’s not so bad, but what you want to avoid are beading sections that when one bead comes off - several dozen more come loose or off as well. Bead showers are no good. Lace sections - check if the missing parts are in really obvious places- it’s very hard to match lace patterns. These problems CAN be overcome, but it takes time and money to do so. If beads are loose, ask the estate people if the fallen-off beads were kept.
For shoes - you want to think of you all in a line for photos. Are the dresses floor-length? If so, less of a problem. Is that maid significantly shorter than the others (and/or you?) If so, less of a problem. If not, see how much of a heel she wants - less than two inches really shouldn’t be a huge problem. If she wants to strut down in lady-killer pumps, then you might want to have a discussion about the style of your wedding and how that might require some adjustment. 
WTF? You’re leaving town… so just call it a “going away party” and invite your friends. Why does it have to be linked to your wedding?
Everytime I’ve tried to reply to this thread, I’ve typed up a long thoughtful reply to people about their good advice, and then my server would flame out. I apologize if people think I’m not reading it.
Lasciel, thank you. I just crossed antique lace dress off my list. I don’t know enough to do it right. This is a good thing and I appreciate your good advice.
You and Nava have confirmed my decision to let my attendents wear the shoes they are comfortable in. I was planning on my attendents wearing tea-length dresses. Floor length it is. My friend who wants high heels wears them everyday. She would probably be uncomfortable wearing flats.
I am certainly not wearing high heels.
neuroman I’m leaving town because I’m getting married. My friends know that I’m getting married. They want to share in my happiness, but many of them cannot afford to take time off to travel to a different state.
(crosses fingers and hits the submit button)
I got married in 1976, the Year of the Bicentennial Weddings. Everybody was doing red, white and blue ::shudder::
I did peach.
You do what you want to do, it’s your damn wedding.
Heels, flats, whatever - I’d let the girls choose their own shoes and would probably go for sandals in July, not dyed-fabric peach pumps. No one will ever be able to wear those again! 
I agree with do what you want - it’s your wedding.
Also, I love buffets - everyone gets exactly what they want, and as much of it as they want.
How are the plans coming, flatlined?