It sounds quite unnatural. I recommend using something like "I like watching football." or "Watching football is my hobby." instead :)

Not bad. I’d probably say: One of my hobbies is watching football.

Yes it is totally ok! You can also say: "I love watching football.", "One of my hobbies is watching football.".

My hobby is .... One of my hobbies is ... The other question is whether “watching football” is a “hobby”. Described that way it sounds too passive to qualify as a hobby. A hobby would typically involve more than mere watching.

Better would be I like to watch football Or I am a football fan