Congratulations on starting your journey towards becoming a guitarist.
There is nothing inherently wrong with the position you pictured. and just because a footstool is a invention geared towards classical guitarist, does not mean that you can't use it under your right foot. Most bluegrass, folk, country and rock guitarist support their guitar on their right knee if playing seated - as you are doing.
However, if you envision yourself playing in a band in the future (where you will likely be playing while standing), you might want to take a slightly different approach to holding your guitar while learning and practicing while seated.
The seated position with the guitar body resting on the right knee is very comfortable. But if you play standing, the guitar will end up hanging in a different position and you will have to re-inform the hand/arm/brain muscle memory mechanism to get used to playing with the different orientation of guitar to body that you will encounter while playing standing.
Electric guitars are ergonomically designed with an expectation that they will need to be comfortable to play while standing. You will notice that most guitarist playing electric guitar on stage, will be standing. Most classical guitarist using a classical acoustic guitar - will perform seated.
Also, electric guitars tend to be heavy and the back of the body contoured (to make it comfortable to play while standing) - so if you don't have it perfectly balanced on your knee, you will be using muscle tension in your arms to keep it from sliding down in your lap.
I see in the picture that you are using a strap even while seated and that is good. But you might want to consider adjusting the strap and your overall body position, so that your guitar is mostly suspended from and supported by the strap. Then the position of the guitar relative to your body - will not change much (if any) when you stand to play. Once your guitar is supported by the strap and hanging in the position you would play if standing, you can raise your knee to support some of the weight just to reduce the pressure from the strap while practicing.
If you do incorporate my advice into your practice routine with an eye towards eventually being able to play your guitar while standing - you will want to be sure you have a very comfortable guitar strap. I like one that is wide at the pooint where it rests on my shoulder.
For a more detailed discussion on practicing with an electric guitar using a strap - read this on Stack Exchange. Benefits of using a strap to practice with electric guitar
Enjoy your journey!