It is was me, I would start building in the current version of WP. Then when 5.0 is released I would update and see if anything breaks. If it does I would see if I can fix the issues. This isn’t really advice, just what I would do.
If you plan on using gutenberg then you might want to consider installing the plugin.
You will have issues. Others are. ACF is not really ready for gutenberg yet. The developer is working on it.
