Hi @BartoszGo,
Moving from version 7.3.1 to 7.4.3 should not introduce any major issues, provided that standard best practices for build upgrades are followed (e.g. handling conflicts, validating customisations, etc.).
You can refer to the official release notes and guidance here:
https://experienceleague.adobe.com/en/docs/campaign-classic/using/release-notes/latest-release
Typically, we recommend planning minor upgrades carefully and using them as a preparation step toward a future migration from v7 to v8.
Kind regards,
Nolan