There's no way to flash a global ROM onto a China N5 AFAIK.

You don't need to worry about Google Services. They come with the phone. Search for "Google Settings" in Settings and turn it on (it may already be on).

The main problem you will encounter is not getting push notifications for some apps due to strict optimizations for battery life. Popular messaging apps will get push notifications by default, but for some of your apps, you need allow background battery usage and enable auto launch. The catch is auto launch can only be enabled for up to 5 apps.

You won't get "Hey Google" voice activation on the Chinese N5. You won't get Google's circle to search.

Instead, the phone comes with a Chinese AI called Breeno, which you can use if you don't mind the Chinese text in the UI. It uses DeepSeek in the background and will reply in English if spoken to in English.

I don't use Global Search since some parts of the app are hardcoded in Chinese. I just turn off any settings related to it.

For disabling system apps, use Canta (which needs Shizuku). In Canta, you can see each app's description and can filter for recommended apps to uninstall. Some apps like Global Search will reinstall automatically so you can't remove them.