I'm wondering if breathing meditation alone is good, particularly for beginners who need to gain strength (the 5 Balas), any views/experiences?
Yes, breathing meditation is always excellent if it's done properly (i.e. don't force or artificially control your breathing; just let it happen naturally). If you make your breathing unnatural, then the energies in your body become unnatural--and then your mental state becomes unnatural.
Another good thing to do is to exhale deeply and inhale deeply 3 times before doing shinay to purify the energies in your body. Visualize all the negative karmas which cause sickness and unhappiness leaving your body during these 3 exhalations, and visualize the positive energy of enlightened Buddhas entering you during these 3 inhalations. Thereafter, just breathe naturally and don't visualize anything. And of course, recite the refuge vow 3 times before your meditation, if you've taken refuge, and dedicate the merits you accumulated during the meditation for the benefit of all sentient beings at the end of your meditation.
What happens if you get sick though?
I know when I had the flu or sore throat pain, breathing meditation became tough -- even painful. Do you guys break practice or just do it very lightly?
I have no problem doing the usual breathing meditation in which I only breath through my nose when I'm sick. However, I do find it difficult to do a special type of shinay which involves breathing through both the nose and mouth at the same time when I'm sick, so I don't do that one when I'm not well.