The answers are yes and yes.
I always ran three brakes on my bike, the coaster can be a little harsh for certain things - manuals for instance. Only back then they were called coaster wheelies..... or gliders..... and most all backwards stuff I never used the coaster.
As for you second question, why would you want to leave the arm off? Fit it and use it
![Wink ;)](http://www.radbmx.co.uk/forum/Smileys/smilies/wink.gif)
Remember though if you leave the arm off, you'll still have to 'set' the coaster first. A tiny crank backwards (a couple of inches or so) just as you're settled before the ramp.
![Smiley :)](http://www.radbmx.co.uk/forum/Smileys/smilies/smiley.gif)