Yes it should be hyphenated.
Can you, or should you? You can hyphenate it if you're moving between lines in a paragraph and need to break up the word. You shouldn't hyphenate it normally.
That is the correct spelling, and ideally it should be hyphenated tax-deductible.However, a substantial number of users do not hyphenate.
McCarthy should not be hyphenated.
not required
A hyphen is not required.
No, in general it is not correct to hyphenate certain prefixes, co-, pre-, mid-, de-, non-, anti-, etc. You therefore write preordain instead of pre-ordain, antidote instead of anti-dote, and midnight instead of mid-night.
Yes it should be hyphenated: co-worker.
Yes it should be hyphenated.
Yes, hyphenate by-laws.
According to the sources I've found on a quick search, you should hyphenate 'coauthor', i.e., it would better be: "co-author".
Your tithe should be 10% of your pre-tax income, NOT 10% of your take-home income. That way, when you file your taxes, you don't have to worry about what needs to be tithed. You should also make sure you get a tax receipt from your church that shows how much you gave, that way you'll get some of that additional money back, since you're giving the pre-tax amount.