Chair are ok serves the purpose.
They will eventually rust when exposed to rain and snow
No problem! Home Depot offers a permanent rental option for just $19.95 per chair, which is a really great option for those who don't want to waste money buying one, at full price.
Yes, the store carries similar feet
Yes, I believe you can. It will indicate in the cart, if you are ordering online. You can also call Home Depot, customer service in your area.