Being that young, fit, and going to the gym 3 times a week, I don’t see any reason for you to be fasting. Just work on eating healthy (avoiding processed carbs, processed food, and sugar), and the metabolic diseases that are affecting so many people won’t be an issue for you at older age.
It’s awesome that you’re taking steps to think of this stuff so early, I sure wish I did. I just think IF is unnecessary with your age and activity level.
If anything, just work on eating the right foods, not snaking between meals, and avoiding liquid calories.
Small weight gain (as you mention) is nothing to worry about in 1 month as it could easily be muscle, your in a caloric surplus if your eating allot but since you go gym, active throughout your day and skateboard too, it’s most likely muscle gain. You only weigh 77kg and for your height (186cm) that’s quite slim (I’m 168cm and 75kg, wouldn’t say I’m fat, just need to cut xD)
If you want to build muscle then gaining a pound or 2 a month is great. Slowly gaining weight when your lifting and active means the weight gain is more likely to be muscle rather than fat.
If you want to lose fat and are really struggling to cut, I’d recommend 2 meals a day or OMAD. Since your able to have such a large amount of kcalories in one meal, just have one extra large meal till your satisfied so your not having 3 unsatisfying meals. It’s an option you can look to ease into like slowly reducing your eating window time so let’s say 17:7 then 18:6.
Anothing thing to mention, what kind of foods are you eating? If allot of carbs then it’s easy to eat more. Having more protein, fibre and fat in your diet will fill you up and keep you satisfied for longer so you aren’t eating more. Might want to make a food diary and keep track of macros for a week or so to get an idea before making changes.
Calories calculator to find out (roughly) how much kcalories you burn: https://www.calculator.net/calorie-calculator.html