In reply to Simos: Accurate foot placement is a fundamental requirement of good technique, keep doing it as much as possible, regardless of grade. Practice it on the smallest footholds for greatest gains.
so;
1. No, do it all the time
2. Your arms may be tired because you've slowed down to increase accuracy, as you improve you'll be able to speed back up (with foot placements) and remain accurate.
3. Yes keep going, no it's not for beginners, it's for everyone.