I think that would be fine. It’s said to be fine to go from dry fasting to water fasting but not water fasting to dry fasting. That in regards to extended fasts. What you are planning on should be perfectly fine and no more dangerous than any extended water or dry fast on its own.
I think this works perfectly fine and if anything it is probably really beneficial for you in terms of your health. Ramadan is truly a blessing and you can make the most of it by doing this and using that time you’d spend eating on better things like learning more about Islam and getting closer to Allah. Good luck and but be careful and don’t be too harsh on your body, keep your sodium and potassium levels balanced. If you don’t feel well, break your fast properly with vegetable broth or soup and ALWAYS seek medical help if needed. My advice is based of personal experience and not medical so DYOR. Though it helped reading medical reports on fasting and dr filonov’s books/research, as well as just taking each day as it comes