The second on is a comma splice because it’s linking to dependent clauses
Ending the adjectives with -ed is not needed, so those answers are out. As for the numbers, the rule is usually that numbers one through nine are spelled out whereas number 10 and up are written in numbers. That said, you do not hyphenate the number with the word, so four-letter word would be correct.
The phrase 'ascribe to...' and 'attribute to...' actually has the same meaning which is 'caused by...' or 'due to...'. The only difference between the two is the kind of connotation it has. The phrase 'ascribe to' is usually used in bad meaning, while the phrase 'attribute to' refers to something in a positive light.