Grammar – Is ‘Till Now, I Was Travelling by Bus. From Now On, I Will Travel by Car’ Correct?

From context it seems clear that you should say

I don't even remember what it is about.

This means that at the moment you do not recall what the movie is about because it has been a long time since you have seen it. On the other hand if you were to say

I didn't even remember what it was about.

Then you are saying that at some point in the past someone asked about about it and at that time you were unable to recall what it was about. This latter phrase makes it unclear whether you know what it's about now or not.

Your last sentence using the future perfect simple tense( future perfect tense) is adequate for the following reasons. 1/It describe an event in the future that hasn't happened and is in no way planned. 2/Said(anticipated) event take place prior in time of the stated time of recollection."for the next year" However, since you used "for the next year" as your designated time of recollection therefore it is slightly more appropriate to use the future continuous tense.(For more clarity and formality)