Yes

you can not say protein is equal to amino acid directly. But, you can say the basic unit of protein is an amino acid.

you can imagine protease A as a pair of metallic scissors, and protein substrate B as a metallic wire. they are both metallic, but structurally different, such that A could break down B. A is very unlikely to breakdown itself, but is cleaved by other proteases, say protease C, a screwdriver

剪刀剪電線會唔會剪撚到自己啊

Protease binding sites are specific to certain AA residues or sequences such that if the active site is structurally far from a suitable cleavage site, self-degradation shouldn’t happen (如果有咁嘅情形應該會演化到唔會畀呢件事再發生，咪下下溶咗自己都幾濕滯) 不過當然有啲蛋白酶可以自行或者畀同類分解啦，thats called autolysis and is important for cell regulation

True

Yes, but you need binding before breaking down, it cannot bind to itself

Protein with a job are usually specialized to do one job only, so no, they can't get rid of themselves just because they are made out of amino acids themselves.

aminos acids are the building blocks of proteins