Most failed app projects did not fail at the build. They failed at scope, at store review, or at the point where nobody had budgeted for maintenance.
Depends on where your users actually are. Cross-platform covers both from one codebase for most business apps; a heavily device-dependent product may justify native. You get a straight recommendation with the trade-off.
Yes, including the rejection reasons that catch first-time publishers: privacy labels, account deletion, permission justifications.
Maintenance is quoted separately and honestly. An app with no maintenance budget breaks at the next OS release.