New journey!!!!

I’m 20 years old, about 400 pounds, (give or take) & I’m looking to lose A LOT of weight. I’m a hairdresser so I’m not too crazy active, I’m on the go a lot between taking care of my grandparents and just running errands. Since my fiancé has started his 5-5 job & I get up with him I wanted to start walking and eventually progress to running a near reservoir in the mornings. The only thing I’m afraid of is sagging skin, any tips on how to prevent it (I know it’s not totally preventable), any exercises, or just tips in general would be helpful!!