It is quite common to create a number of different files for different purposes.
Apart from different colour mode for print (CMYK/spot) and web/other screen uses (RGB), obviously print requires higher resolution, and web/other screen uses require raster files.
The resolution needed for web/other screen uses should be evident in each case.
The resolution needed for different print tasks depends on a number of things, including kind of printing.
In this connexion it is important to realize that the required resolution in print depends on size and viewing distance: if you view artwork that is twice the size at twice the distance, you will need half the resolution, in other words the same file size in pixels by pixels. You may say that the required file size (pixels by pixels) depends on the viewing angle.
This means that a billboard to be viewed at a large distance and a normal page may have the same file size; obviously, the file size for a business card may be smaller.
Apart from all that, it is possible to recreate a photo like the leaf as vector artwork in Illustrator, and have everything as vector. If you consider that an option, you may post in the Illustrator forum to get started, and/or look round for tutorials; specific ones may very well be sugested in the forum, probably by others over there; it is past midnight over here.