Spanish language Q&A Forum

I am confused after getting an answer wrong in a test and then reviewing the subsequent lesson.   

In a recent test, this sentence was given to complete.   "No me gusto nada hacer ejercicio _____________."  My answer was "después de comer," when in fact the answer was "después de comiendo."   

I went back to review the lesson and the lesson states that after the preposition "de" comes the infinitive form of the verb to say the "ing" form of the verb.    Now I am confused as to why my answer of "después de comer" is not correct.   When do you use the infinitive?  and when do you use the present participle (i.e. ending "ando" or "iendo") after the preposition de?

When should we use pues versus porque? In the text it was translated as "because" = "pues". Thank you!

If the construction starts with “si prefieres X....” isn’t “si preferías X...” also correct?

Is "suficiente" known more for "enough of" just like adequate and is bastante more known for "plenty" like enough, but more than just enough? I saw a native say suficiente go on about how they use suficiente=enough and bastante=plenty. I believe you can use suficiente before and after the noun, although with bastante is it only before the noun?