(저는) 영화 보고나서 저녁 먹을거여요.
~하고나서: after 저녁: dinner
of course '저녁식사' means dinner, but it isn't followed by the verb '먹다'. It is followed by the verb '하다', which means 'eat, have', not 'do' in this context.
It depends, but in Korean we omit the subject of a sentence much more often than you do in English. Otherwise, the sentence is likely to sound very unnatural in many cases.
I'm sorry, but I have no idea what you mean by 'location marker?'.