I live in the UK and I don't have a garage either, I'm fortunate enough to live on a quiet enough street off of main roads though, so I do all my maintenance on the street. It's ok until the wind gets up, and genuinely pleasant in summer.
So far as being vulnerable - yes you are. This is something you have to come to terms with, there are many biker safety courses out there designed to make you a better rider, police riding courses are very good, and so are some advanced ones - they'll teach you how to ride defensively, how to read the road as best as possible, danger assessment etc. That said, there is always a chance something out of your control could happen to you, but the same could be said for walking out of your house every day, we do what we enjoy because we enjoy it - you must assess the risk vs reward and decide if it is for you.
My advice? If you honestly have an interest, try a beginners course, even if you don't initially intend on getting a motorcycle it will give you a little taste of what it is like and let you make a slightly more informed decision.