One amplifier failure mode is to pass DC current out of the speaker terminals. You’d get cone/voice coil slam that could be damaging depending on the speakers and the amplitude. The protection circuit should cut in, but no system is perfect.

I mean, they’re plenty heavy enough gauge. The ends are a bit sloppy. Personally, I’d either tin them if they’re going into spring terminals, or crimp on some spade lugs/install some banana plugs if there are binding posts.

Not separates. It’s a combo amp/cassette unit. Wouldn’t pay more than about $40-50 US for one.