Is it possible to
1. Load a simple splash activity A (which displays basic app info)
2. Utilize the time to load activity B in background (with elements which take a longer time to get ready like populating CLV, Spinners etc from SQL)
Not really if the other Page is an Android Activity (take a look at the Activity lifecycle).
You can load the data in the background into classes (put the loading code in a service). But that will not allow you to populate visual elements. But it may be ok with lazy loading.
OR
you can use panels in one activity, but then B4xPages is a much better way of handling this.