If weather is fine and ground not muddy then it should be barefeet so I they are all the same. If they want to slip in and out of flip flops then that might be a good idea but what harm can barefeet be for a while.
I agree leggings is fine and also good that you are getting to try classes out first before going to any expense.
Looks like it will be barefeet if they don't allow socks.
Whenever I can practice I do. I don't do set times as work can get in the way.
I agree that arriving early for a class and warming up if possible is a great help.