Past tense stress
In the past tense, ex. 'él habló', do I put the stress on the last syllable whenever it is accented? Or is the accent only there to distinguish it from other forms, such as '(yo) hablo'?
Always count on accents. They mark the stressed syllable in unexpected positions (the expected stress would be "hablo"). The only exceptions could be interrogatives vs relatives ("quién" vs "quien") but it seems like the interrogative forms have an independent stress and the relative forms are unstressed and attached to the next word. Ask to a native speaker to say "Juan, ¿quién es tu amigo?" and "Juan, quien es tu amigo, ...." I can't tell it, because that information biases my perception.