I guess my reply is coming after your D-Day

Still if this could be of some help, I will be obliged.
Let's take your questions one by one:
1. 'Or' and 'Nor' are not interchangeable. Moreover if you will read the 2 statements carefully you will observe that why these 2 conjunctions are not interchangeable. In sentence 1 try to put 'or' in place of 'nor' and in sentence 2 try to put 'nor' in place of 'or'. You will notice that the meaning of the 2 sentences will change completely.
In GMAT give a special attention to the meaning of the sentences.
2. Grammar rule states this structure : if present tense, then future tense. Therefore nothing wrong with the example that you have quoted. 'could' can be used in the present tense. 'Can' is also applicable in your above sentence.