Thanks for your feedback! First, regarding zoom:
Regarding font size, you should file that at adobexd.uservoice.com. I don't see an existing story quite like it, and we'd like to see what you'd like beyond the current drag for point text and the numbers in the property inspector.
Regarding prototyping mode, you can actually link to a page outside of current view by creating a wire anywhere, then in the drop-down, selecting the name of the artboard. There are some refinements that have been suggested in UserVoice, so you might want to search through those and see if there's one that reflects what you'd like outside of this workaround.
Guides and rulers will be coming in significant chunks over the next couple of monthly releases. You can add your thoughts and stay up to date on our progress here: Ruler and Grid Guide – Adobe XD Feedback : Feature Requests & Bugs
Hope that helps!
When will this app be available for Windows? I see that you have it for Mac users and not Windows users
As we've mentioned in a number of different places, we're aiming to release Windows later this year. We're currently working on it, so hang tight!