Why is focusing on the breath more difficult than focusing on Mantras?
Mantras are more interesting than the breath.
The breath is much more stiller.Mantras have obvious movement.(Speech or mental verbalisation).The mind easily latches on to mantras.Which is why you can find yourself in a trance like state (tranquilising state) much more faster.
How important is it (Focusing on the breath) before vippassana?
Very important.If i can't focus on the breath which is gross and physical (at the start) i won't be able to focus on the subtle movements of the mind. Focusing on the breath trains you to develop concentration.You need concentration to practice vippassanna.To what extent you'd like to develop concentration is up to you but generally you need some form of concentration for vipassanna.
What is the difference between the results of breath vs vipassana?
Focusing on the breath develops concentration.Focusing on Vipassanna objects develop insight.You can still use the breath to practice both concentration and vipassanna.Your just focusing on two different aspects of the breath.
I can hardly do 10 conscious breaths (feeling peace). Any suggestions for betterment?
Do 5 conscious breaths.If you can't.Do 3 conscious breaths.Master that.
When you can do 3.Then slowly add 1 conscious breath and then another. Until you reach 8 conscious breaths.don't do 10 conscious breaths that's too long.It's not about the numbers it's about the quality of your attention on each breath.Please feel free to find a number that suits you.
In mantra meditation, it feels like something (kind of waves) is coming out of my body.
This could be piti (rapture).Piti is what makes the mind stay with the meditation object without feeling forced.Because it's pleasurable..Otherwise you'll have to rely on good old effort (Vitakka).which is why it's easier to do mantra meditation.Piti is generated faster.With breath meditation there is also piti but that "waves coming out of the body" feeling.That is way too agitating if your using the breath.There is a lot more happiness in the stillness of the breath.