Agreed but you should listen very carefully to the sound you are producing especially if the guitar driver is housed in an open backed box.
Yes but as BassmanPaul said listen. Bass notes can cause excessive voice coil movement. In a sealed cabinet this is somewhat suppressed.Not in an open cabinet. If the lower notes are distorted or start ok and finish with a quick buzz, lower the volume.
Entirely up to you. Quiet practice good, rocking out at home maybe breaks the speaker. When we tried my bass through the guitar player's stack it was a feeble sound and then it farted out so that was that.