#1: it really doesn't matter. Many people use their rescue inhaler prior to exercise, but you can take your maintenance inhaler any time you'd like. You might experiment and see which way works best.
#2: again, it doesn't matter whether you inhale through your nose or your mouth. If I'm just strolling around, I inhale through my nose; if I'm really working hard, I inhale through my mouth. The important part is exhaling through pursed lips. I always use PLB when I exercise, from the very beginning. It helpsme delay the time when I begin to get sob. Practic PLB until it's second nature and you do it all the time when you're exerting.

use your inhaler before walking, a rescue inhaler if you are struggling after walking. Pursed lip breathing is always helpful. In nose out lips.

thanks for the info. i want to get the most out of my medicine and exercise .I've been having to work around real dusty areas so i make sure i wear at least a n95 or better mask . they fit good and do a good job keeping dust out of lungs

I am waiting to see what the answer is.