...not unless you're in the habit of putting your ear to your cainet. 300 watts may be alot of power to overdrive, but that's also 300 watts for bass. Low end eats up volume. It's not going to fry your ears with midrange like a 45 watt JTM 45 Marshall.
...not if you want SVT tone. As I said before, it's loud, but it's not a guitar amp. You've got much more to worry about from the acoustic noise of your drummer concerning your hearing.
NO!!! There are no 300 watt attenuators and be glad there aren't because they are a one-way ticket to dead power tubes; they work an amp WAY harder than normal use and can do some serious damage to an amp, even when used "properly."