It will depend on a number things, one is your theme.Team, could some one help us out?
You need to use custom CSS and be mindful of it's placement to change it's look and behaviour, and all that depends on the theme you are using.
Also, putting it in the footer is a terrible idea. You really should put it in the header. If your theme won't allow you to do that ... you need to get a decent theme, even if it's a paid one. I recommend Flatsome.
It depend. If you put the currency switcher in the middle of the screen, it will be annoying. But putting it in the footer is not really a good idea as not all visitors are looking at the footer. There are many locations good for the currency switcher that is not evasive but effective.'m using Flatsome at the moment. It's in the footer just for the sake we don't want a currency switcher all in your face all the time.