Hi Sylvain,
I will try to answer your questions based on a previous project of mine which was a native mobile offline app.
- For making offline work in your Mendix app you will need to work a little harder and different than used to in a responsive app. But this is mostly in the model area and object synchronization where there are some restrictions. Generation pages for responsive and mobile will work fine mostly.
- Things like reference set selectors usually have quite a different styling in mobile than in responsive. These, like other ‘selection’ pages usually have to be modeled out with microflows and listviews to make them work nice and without pop-ups.
- The performance drawback depends on your end solution. In our case, we had the *->* relations for responsive and reporting and made use of extra 1-* relations for mobile. In event handlers on the entities used, we kept the model in sync are created the extra needed objects or set the proper associations, based on the source of the change (responsive or mobile). The impact was minimal and not noticeable to end-users.
All in all, I think you're on the right track. What was/is a drawback for most of us, that we're used to modeling for responsive and then had to ‘learn’ how to model for mobile, maybe won't be an issue for you because everything will be new.
Wouter Penris shared their team experiences building an app that might give you some more insights on certain limitations in Mendix offline mobile and how to overcome them. https://www.youtube.com/watch?v=7pLKirIirsI&ab_channel=BLD
And there are some experienced experts in the Mendix Slack #native-mobile for any quick questions or sharing insights on certain topics.