Go go go!
I will go hiking with you one day
Old puppies at vets is hard. It's always a little scary. Let us know how it goes <3
It should be snug as in your band should be supporting you, not the straps. So...it should lay flat and horizontally, shouldn't slide, shouldn't ride up or down, it should stay put. It also shouldn't dig in, though

Pull it tight when measuring, because you want to buy a bra that is snug on the first hook, because it will loosen over time anyway.
http://wellfitting.com/pages/how-a-bra-should-fit