In 99.9% of the use cases, there is no simple answer to "how can I make a photo look like this illustration/painting style." And in fact, for most styles it would entail many various techniques to get even remotely close to an illustrative style. There are many things which take half a second with an hand, brush, and paint but can take much, much longer to create digitally. Sure, it may be possible to get close to a single brush appearance, or a single color appearance, but as a whole, you'd need a manual or book for each and every photograph you want to use.
You would be better served by determining what techniques you feel comprise the style, then try and replicate those techniques individually digitally. Ultimately combining several techniques for a final image. Otherwise, what you are asking is for someone else to do all that work and post a description of how to recreate every possible technique and variation... which ultimately won't be correct for every photo you may want to use.
Style is often created due to the artist's use of brush/pen pressure, direction of painting, pigment, medium texture/grain, and "happy accidents". I mean one can not accurately predict how painting over one area may alter the paint under that area. Often the results are anticipated, but ultimately random in nature within a given spectrum. This is especially true for watercolor or medium that are semi-opaque in nature.
In order to try and replicate an illustrative style within a photograph one would need to be detailed, planned, and meticulous with every single aspect of the photograph. And the photograph itself would play a huge role in the final result.
There's nothing which is going to work by running a few various filters or effects on an photograph and mimic an illustrative style in most instances. If all styles were boiled down to a series of filter steps, then there would be no need for any artist.
So, you need to experiment and determine which areas comprise the style you are seeking, then search for methods to recreate those aspects. For example, grain....
But as you can see reviewing that, it's not an easy, one step action in most instances. So one would need to be methodical on how it's used on a photograph - extracting portions, creating the visual effect, then extracting other portions, etc.
Face it, if all art were merely boiled down to a series of steps.. there would be no value in any art anywhere. You are basically asking.. "How can I devalue this artist's style/technique so much so that it can be recreated by anyone with software." That's often not easily achieved. Actually it's almost never achieved when comparing actual illustrations/paintings and photograph manipulations.
Your time would be better spent determining your own steps and procedures and creating your own digital style which may be merely influenced by an artist but doesn't try and mimic that artist directly.