I like it. Very clear and simple which is perfect.

You could provide it free and open source as it is now. This would be a good way to gain users/subscribers. Just ensure they use real email with a confirmation link to download it. The more subscribers the better as it's the best marketing strategy. When you are ready to launch the trading functions you will have an audience and a % will upgrade for a price. And yeh the upgrades cannot be open source.

Open source all the way is brilliant for all concerned and will gain many users/subscribers to sell something else to in the future but only if you have other forms of income and set up financially to do it.