That's why they usually place Buks on mountain tops (usually on antennas) and at the airfields. A heavily fortified objective usually has 4xDefensive Convoys on it (4xTors, 4xSA-13's/Chapparals, 4xTanks, 4xAAA), manpads in the wild around it and a Buk system on top of its antenna
not at all
if you've wasted all your MPU's on Buks, it's quite a challenge to destroy a Tor
they're much more pain than the SA-8's for example
Kh-25MPU is not an ultimate weapon at all. It still misses often if launched at <15km. Moreover, SA-15s always try to shoot down the missiles (though not really effectively). I saw them shoot down the mavs.
there are many ways to kill Shilkas in a Su-25T, they're easy targets indeed, but you'll have to deal with the radar sams first
there's no way you could destroy a well fortified objective in one sortie in a Su-25T
not at all... they often hit you from the front or from the sides when you don't expect them... from the back - yeah, they miss, IR jammer helps, flares as well
a well fortified objective can take a whole day to destroy it (without any air resistance). Dean from Red team has proved it many times.