I would not advise taking physical barrier. It can work out alright if you overcast, but overall it makes relatively weak armor/barriers, that will go down very quickly in a real fight. With 15 spellcasting dice (assuming a R4 Power Focus), you're likely to get only 5 hits or so. That's adding 5 armor to whoever is behind the barrier, which is nice, but hardly worth (imo) the 5 DV you're going to be resisting from casting at 5 force. Especially as it works both ways, protecting the enemies against any shots originating on the inside of the wall! Additionally, if your GM counts damage going through the barrier armor as also checking against destroying the barrier, you've got a barrier with 10 armor dice and 5 hit boxes, likely to go down within a single round of combat.
Same kinda goes with mana barrier. If you're worried about spells, you'll want beefier counterspelling. Spirits will whiz right around or straight through your mana barrier, even if fairly overcast. If it's other mages you're worried about, the point at which you have time to raise a mana barrier is probably when you should be overcasting a nice little stunbolt their way, or a nausea spell with a body-based check, to incap them.
