I have only visited Whiterun, Riften, Solitude, and Winterhold for the major cities, and have just started recruiting for the Blades (just one person so far). I was considering also starting the Civil War quest, to have them run parallel. Is that a good idea, or should I wait until I finish the main quest, or is that not a good idea? I decided to select the Imperials this time around (it is my first time), and was wondering when that should be started, or does it even matter?

Please try not to use any spoilers if at all possible. Thanks!!!

Doesn't matter.

You did not need to make another thread for this.

How about making separate characters so you can try any number of combinations for these quests?