I've never heard of people getting their second or third choice but if they give us the option of choosing them there's got to be a reason.
There should be options everywhere you go but you're probably going to attend the church of your host family unles you specified that you need a place to go to church on your app.
It depends on every host family but unless they have a teenage kid or something, probably not.
None of the other programs let you pick your city or country, so I doubt it.
Hope that helped!