It's a matter of choice. Past tense can provide a sense of distance and perspective, while present tense can heighten the tension and urgency. You could even experiment with both in different drafts and see which works best for your novel.
It depends on the style and genre of your story. For most fictional stories, past tense is commonly used as it gives a sense of telling a completed tale.
Hard to tell. Maybe you discovered a hidden secret, or perhaps you formed an unexpected alliance. Without knowing the comic details, it's a bit of a mystery!
If you didn't include too many unnecessary details, then it was probably fine. But if you rushed through important parts, that might be something to work on next time.
It depends on the mood and style you want to create. If you want a sense of immediacy and action, present tense might work. But past tense often gives a more traditional storytelling feel.