Answers to your questions:
1. If task A depends on only tag 1 and task B depends on only tag 2 I think it's better to create to different scripts. It makes script more readable.
2. I think yes. It's better to place all these tasks in one script.
3. Yes, the putting tag inside "if" will affect on the script. If value of this tag is changed this script will be executed.
4. The best way is place this task in one script and use "if" operator to execute the conditions you want.