First question: I have been extensively using the same vector image in different sizes and colors. 
To achieve that, I was simply creating resource each time I needed unique size/color combination. 
However, I realised this is probably a lot of space "wasted" for the "same" image. 
On the other hand, I was doing some research and apparently it is quite CPU-intensive if you are modifying each vector in the layout itself.
That being said, I am wondering which is better approach: having single vector and resizing/recoloring it according to needs or having one vector for each needed configuration?

Second question: same layout on different devices.
At first I thought that using same "dp" values automatically gives you same look on different devices but (obviously) I didnt' account that screen density and device size are also important factors to consider.
That being said, I was thinking of using "smallest-width" (SW) resources and defining layouts in these. 
Is this approach (using SW) approach you would have taken to achieve same layout on different devices or am I missing something?

Third question: constant variables in Kotlin.
What is the difference if I define const variable as top level (above class) or inside companion object in a class?
Because as far as I know the only difference is accessing these but recently I was woried defining them one way takes more resources compared to defining them the other way.

Next question is a little bit connected with SQL.
As suggested I have been using prepared sentances to manipulate my SQL base when dealing with user-input and "normal" setnaces when dealing with pre-defines things (such as resources, ...)
However, I have recently remembered that in rooted devices one has access to internal storage so theoretically one could temper these and by doing so inject things into my database.
Should I be woried for these and change everything in prepared statements or am I overreacting by thinking this?