From which box?
yes
Yes, a 30 amp breaker is a 30 amp breaker. It must however be able to fit the box it is installed in.
You can measure the electrical current with an amp meter. Amperage measures the current flow.
There is no such thing, 30 watts is 30 watts. "Line in" is normally about 1v peak - to - peak. So if your 30 watt amp has a "line out", no problem. An amp can be modified to have a "line out". Similarly, an amp can be modified to accept larger inputs without damage. However, driving an amp straight from the normal output of an amp, although possible, is fraught with danger and expensive consequence and should be avoided at all costs
Line 6 Jam amp
Adding a 220V line to a 150 amp panel is feasible, but you must ensure the panel can accommodate additional amperage. Consult an electrician to confirm if the panel has available space and if it meets the necessary electrical code requirements for the new line.
If u mean amp as in amplifier then it wont be possible to add one with the stock CD or tape player. if u want to add a sub then just get the wires from ur rear spealers and hook up some subs to then instead of the stock speakers.
yes, you can attach. but if the current through the line i.e. through the breaker exceeds 20 amp the breaker will trip. As long as the line carries 20 amp or less there is no problem.
To run a monitor speaker or to connect several amps in series to pre-amp your amp.
Yes, it is possible to plug a microphone into a guitar amp using a microphone input or an adapter.
You can either run a patch cord from the "line out" jack on back of your amp to the board (or head of the snake, if your band has a snake for the PA). If your amp doesn't have a line out jack, you can place a mic in front of your amp, and plug it in to your board.
If your amp has a "line out" jack (most likely on the back of amp), you can run a patch cord from the line out jack to an input jack on your mixing board. An earphone jack will work also, but not quite as well, as that is not what it was specifically designed for.