> -When is a Mac requested during the overall process?
Currently it's required when uploading to the appstore. We hope to remove that requirement in the future. You can use services like Mac In Cloud to perform the upload stage.
> Is the only way to build the distribution binary (release) app
package (and the debug one) to give my Apple developer credentials and
certificates to the CodenameOne server?
Apple developer credentials are used for the certificate wizard. This helps you make a certificate/provisioning that's compatible with Codename One without a Mac. We don't keep the credentials and don't care about them. You can do this manually but it's a very hairy process so you'll be on your own if this fails when you try to build the final app. There's a bit of information on that in the developer guide.
Regardless of your choice above... When building you need to give a certificate, provisioning and the password for the certificate. Since this password only applies to the certificate (it isn't your itunes password) this isn't a big deal.
> -Is it possible to download the package and then upload it manually to the App Store?
There is currently no other way. You can **only** download the package and upload it manually to itunes.
> -Is it possible to debug on real iOS devices connected to a Windows machine, transferring the package by means of iTunes?
"Debug" means stepping over code. From your text I assume you mean run.
You can do this much more easily. Just click the OTA link or scan the QR code. No itunes required to install on your device (notice it needs to be registered in the provisioning...).
You can also debug but for that you need a Mac and basic or higher subscription. You would debug the native generated xcode source code.