In PHP, use the sha1 function. For example, to encode the word "hello" into sha1, use sha1("hello");. Similarly, there is a base64_encode function. So you'd use base64_encode("hello");.
Could be any base from 7 upwards.
Tetrasigsimal
There is no way to tell, since adenine is a purine base, but not the only one. Cytosine is a pyrimidine base. So it can be anything from 0 to 112!
nothing should happen.
Acid into base!