We have quite a bit to go before multiple floors would go default so that’s not of any immediate concern, continued bug fixing around, especially remote stands, will of course be an always big priority.
No, you should be fine with just a paved default runway!
This might very well be the case, enabling proper overtaking for service vehicles is quite experimental and there was also a few other fixes and changes in -6 that might affect other parts of the simulation. That’s how it is sometimes on the experimental branch, we find a bug that is caused by a certain behavior, we patch that bug and run a bunch of tests on the affected save but then also on a few of our own default airports to ensure that it’s not immediately affecting the overall functionality. However, given the fact that there are so many changing variables in Airport CEO and that there is an insane amount of combinations regarding how airports can be built and simulated its very difficult to uncover all cases in which a new feature may break.
So that’s how it goes, we fix bugs, sometimes we fix bugs with more experimental solutions and they may end up breaking a relatively “stable” experimental build, we then patch those breaking points with the help of bug reports until we’ve again stabilized the versions including the initially experimental solution.