Issues on ui5 bootstrap

1. Why ui5 would download the library-preload.js, library.css and library-parameters.json?
2. Can it be avoided? Coz this will require too much to download and also cause the latency of the app performance?
3. Can I customize the size of a ui5 module from the server?

For example, if I used 10 controls in sap.m, I just want these 10 to get downloaded instead the whole sap.m
I tried the data-sap-ui-preload="async", but it would download all controls used one by one. This would cause a number of requests that would finally impact the performance.

Victor