From my experiences every migration can be a little different even if it looks like the same setup of farm and environment. What I always do and recommending to You now is to do Test migration. You can check everything what you think could be problem after migration process.
But I think that your Webparts and Master Pages will work correctly and there won’t be any change. You should use Upgrade-SPsite command on SP 2016. https://docs.microsoft.com/en-us/powershell/module/sharepoint-server/Upgrade-SPSite?view=sharepoint-ps
Besides here are some notes for site collections upgrade: https://docs.microsoft.com/en-us/sharepoint/upgrade-and-update/troubleshoot-site-collection-upgrade-issues