If I decide to become a crown player and open all the worlds in the game. Then, I decide to become a subscription member. After my subscription is up, will those worlds that I previously opened when I was a crown member still be available?
Once you purchase a Zone with Crowns, it is open to all characters on that account forever.
Each character on that account will have to unlock access through the Spiral door by progressing through the story but the Zones you have purchased on that account will never have to be purchased again for any character current or new on that account. This persists, even if you switch back and forth between being a Member and being a Crowns player.
I have another question. Is it possible to get a chart or be directed to a chart showing a difference between having a crown membership and a subscription?
Whether you purchase a Membership or Pay by Area, really depends on how you think you will play the game.
If you plan to push through as much of the content as possible in the shortest amount of time, then a month to month Membership is the best value for you.
If you plan to play several characters over a long period of time, then a 6month or 1year Membership is probably the best value for you.
If you only have a few hours a week to spare, or will hold off playing for long periods of time, then purchasing individual areas is the best value for your time. It allows you to purchase just the next street you need to progress, and once you've purchased an area, it's accessible to all your characters on that account. Purchasing individual areas lets you progress at your own pace without feeling like you have a Membership hanging over your head.
If you're not sure, then use the Free to Play portion of the game as your guide. See how fast you move through to the end of Triton Avenue, and gauge your passion and your available time accordingly.