Low CP-High IV & High CP-low IV

if you can wait any longer, wait for around lvl 30, catch high cp/80%+IV and save the dust.
I regret spending a lot of candy and dust before reaching at least lvl 25+

This depends on the distribution of Pokemons in your area. If it's like here I would safe the rare hard-to-come-by like Exeggcute and Charmander until I catch better ones with both high level and good IV, but already evolve the more common mons like Jiggly, Eevee, Tentacool and Nido with the highest CP to have something for gym fights

Actually, Pokémon with more than 50% IV are suggested, the best if above 75% IV.

Just another perspective, why waiting?! Just go for it to enjoy the game your way...

After all, it's a game... As far as you enjoy it, it's a good strategy I think.

P.s.: I did regret for some mistakes along the way. But it's more fun rather the waiting all the times for this and that...

How rare are the candies for you? If you can find some of these easily in the wild like evee or nidoran I wouldn't hold off evolving it because you can easily collect enough candies again. But I wouldn't evolve anything lower than a level 20 Pokemon as that's the cut off for eggs. Since star dust is valuable I would wait.

For the more rare stuff I would hold off because as you level up you find better CP Pokemon with good IVs or you can wait to hatch a good one from an egg as you level.

I'm a hoarder so I tend to save candies even for common Pokemon and don't evolve anything unless it's 90+ % IV but that's just me. Sometimes I make exceptions for Pokemon that I really want in my Pokedex but this game should be fun so just evolve what you want and don't worry so much.

Movesets tend to be more important anyways so if the candy is easy to get for you (like Eevee and Growlithe for me), I tend to just evolve away and use any that get the right evolutions or movesets.

I have transferred many 90+ Arkanines/Jolteons/Flareons due to bad moves...

With how prestiging works, I am also looking very closely at mid level (10-15) mons since once you have a stable group to attack with (usually lvl 20+ due to eggs), the level 5-10-15 mons are actually more important to find so you prestige faster for max prestige.

Unless it's something pretty rare like Snorlax or Lapras/Dragonite, I wouldn't bother powering most things up since you will tend to find very usable ones as you level up (I'm 26)...even if their IVs are very bad.

Exeggcute's are pretty rare for me so I didn't evolve one till I had a lvl 20+ one...I didn't care as much for IVs since I needed a water counter.

lv 23, stardust is not your concern

Evolving those high CP pokemons you have now and enjoy the game by fighting and training gyms.
But save your stardust for high IV, high CP pokemons you may catch later. I only use stardust for my Dragonites, Snorlax, Lapras and Gyaradoses.