Ho-oh's Scared Fire move is extremely damaging, and it's recommended that you train it as much as possible. It'll prove a useful member of your party. You only have one chance, as I mentioned earlier. In my opinion, Lugia is much more powerful than Ho-oh, since it IS a Psychic type Pokemon. Entei, Suicune, Raiko - One of the most sought out Pokemon in both Gold and Silver.
Most people never get the opportunity.
Now, about catching them. It's pretty simple, but tricky at the same time. Now, this is the hard part. By the time you get to where they were, they've probably already moved to another part of the map. What you need to do is manage to corner them in a corner of the map where they're unable to go anywhere else.