I can definitely see why the om would cause confusion.
In this example, vi åker om en timme, the om is used as a regular preposition, which is usually translated into English as about. But in the case of leaving, English uses leave in an hour, and the about in leave in about an hour would make the phrase mean to leave in approximately one hour.
For vi tycker om, the om is used as an adverbial verb particle. Put simply, whenever the word tycker means to like something, it always requires the word om as well.
If you'd like to read more about tycker om, there's an excellent explanation here: https://www.duolingo.com/comment/5892480
I looked up 'adverbial verb particle' just to be sure what you meant: "Many words can be used as both adverb particles and prepositions. There is some difference between an adverb particle and a preposition. While the particle is closely tied to its verb to form idiomatic expressions, the preposition is closely tied to the noun or pronoun it modifies."
No, you cannot. In this context "åker" means leaving and not being in the middle of the journey, that would be "reser". Plus, travelling is more of a continuous action than leaving, so I don't think it sounds right to say you're travelling "in an hour". It'd be either "travelling for an hour" if you mean duration (which is not what the Swedish sentence means) or "will be travelling in an hour" if you mean to say you'll be in the process of travelling by the time an hour has passed.
gå is a very versatile verb, and it can mean both "walk" and the general-function "go". Hence, you can use it virtually always when leaving.
But åka is not as versatile - its meaning is restricted to "go by vehicle". Hence, if you use it to say you're leaving, you can't mean that you're walking.