[poulsbohemian]

Why do you want this app you are building to be cross-platform?

You've shared technical requirements, but you haven't shared business requirements. You should ask yourself whether you can actually achieve your business / user ends with a cross-platform approach. The three platforms are unique and users across the three have different expectations. For example as a Mac user, unless the software is super specialized such that there isn't any competition, a native Mac-focused solution will always be preferable to something that "kinda sorta" looks and acts like Mac software.

Without knowing the purpose of the software you are building, one has to really wonder if it needs to be native or should rather be a web app (for example), or even mobile first or tablet preferred.

Just some thoughts.