If they happen more often, will it become easier for me to initiate my own lucid dream?
Short-answer: YES. Long-answer: no, because there are ways to improve lucid dreaming frequency (by using substances like galantamine for example), and those artificial aids will not improve your lucid dreaming chances if not for the very short-term. On the other hand, if you use techniques that are linked to reports of lucid dreaming improvement, then yes, especially assuming if you increase your practice to a satisfactory (don't ask me to quantify it ) level, and maintain that practice. Just to give you an example, I've stopped practicing more than an year ago and I still occasionally experience them. But if you manage to keep the routine, you'll increase the chances of achieve more lucid dreams - not only due the improve results that the techniques provide you, but also because you'll become familiar with your own dream world, identifying more cues, and even because you'll be more primed to react "lucidly" in your dreams.

- Does visualizing things in a Lucid Dream help you improved your visualization skills in real life
" It is important to note, however, that imagery ability is not a fixed characteristic. It can be modified with training and experience (Hall, 2001; Kosslyn, Brunn, Cave, & Wallach, 1984) and, while the capacity to image varies between individuals, there are characteristics that can be improved" Source.

Do notice though that there's no evidence (at least that I know of) between mental imagery ability levels and lucid dreaming visualization skills. In fact, it may even be functionally complicated to test it, because as you may realize, the own self-generating nature of alteration of dream content might compete with such process...even more intentional action.

Anger cause stress. If you're super stressed in a dream, does it affect your real life health? I remember dreams where I was angry and when I woke up, I was very stressed because of that.
Most likely a non-issue, unless you're experiencing a high dosage of stress or continued stress: stress by itself is not harmful, is just the continued/acute exposure to it that screws things up. If the above cases are true though, stress is probably just a symptom of a underlying issue you might be experiencing.