#1: Yes, but you should do it intelligently. Not teching in the air lets people continue their combo. Not teching on the ground means your opponent can potentially OTG you into a brand new combo. That said, you shouldn’t roll or quick getup heedlessly - get in the habit of neutral teching (button + no directions) and blocking until you understand when it’s safe to try to quick get up or roll. Air teching is generally safer, so you should do so ASAP, just be wary of mashing - it doesn’t do you any good to air tech, get out of a combo, mash out a jumping attack and get CH’d into a new combo.
#2: Barrier guard has four major applications:
A) It pushes the opponent back far more than normal blocking, so using it will cause your opponent to eventually need to dash in to get close enough to continue attacking, or to risk whiffing an attack due to being out of range. Either of those events will give you an opportunity to counterattack or escape.
B) It’s crucial to blocking in the air - most ground-based attacks cannot be airblocked without using barrier.
C) Barrier guarding can prevent you from being guard broken when you only have one primer left - if you barrier guard the attack that would have broken your last guard primer, you lose ~1/3rd of your barrier gauge, but you don’t get guard broken.
D) Barrier guard prevents chip damage. This is handy when you’re low on life, or just in general when blocking an attack that does a lot of chip damage.