Yes, believing Mormons in general follow their own rules.
No. It was clarified to mean caffeinated hot drinks. So herbal tea and hot chocolate (well, okay, I know chocolate is mildly caffeinated, but it’s still okay unless you’re being ultra-hyper about it) and hot water are all right.
Well, people wouldn’t in general know (in general I don’t imagine you’d be getting undressed in front of a bunch of people), but your spouse would, and if you were both believing Mormons that would probably lead to some friction.
I guess I would say that if you believe Mormonism, then you are happy to obey the rules because you think it is what God wants of you. If you don’t want to obey the rules, then in some sense you can’t call yourself a true Mormon.
Although I should also discriminate between not wanting to obey the rules and trying to obey the rules. If someone were addicted to tobacco and was having a hard time kicking the habit, but really wanted to stop, that would be different than someone who just happened to like coffee and drank it all the time even though they knew they weren’t supposed to.
You would be able to go to church, and you would be able to hold a calling and participate in the life of the church in most ways. However, you would not be able to get into the Mormon temples, which is the mark of a true believing Mormon.
(I also am not able to, even though I don’t drink coffee, because – as you might expect – in addition to rules about alcohol and so on, there are rules about what you must believe that I am not able to answer in the proper way. So in some sense I am an example of what you ask in your question – I go to church, I hold a calling, I’m in the choir, I visit teach another woman, I basically do everything another Mormon would do… except go to the temple.)