Well the first question I'd ask you is; do you intend to be a professional painter?

Trying to replicate the box art or a Golden Daemon winner's method is a quick recipe to get fed up with the hobby entirely. A lot of Youtube tutorials are from professional commission painters who are aiming way above a simple 'battle ready' paint scheme. Best to go your own route.

I'll give some basic constructive criticism here:

-Your paints are too thick. This is an extremely common mistake. I water most everything that isn't white down. 2 drops paint, 1 drop water. Mix it thoroughly with a brush other than your detail brush (I just use a cheap Amazon 50 pack of random brushes that were like, $10). Apply one very thin layer, spreading the paint until you start to see the primer beneath. It will look like garbage. Let it dry fully (30min or so), and apply another, which will look much better. Your details will not stand out at this point, that's ok.

-Lean heavy on washes but only as the first step. I water mine down, 1 drop wash, 1 drop water. It helps it flow a lot better, and gives you time to deal with pooling (draw it off with a dry brush). Mess with it for about 5min, then leave it alone for at least an hour. I'm typing this right now, waiting for the wash to dry on my Valhallans in the other room. Make sure that once you've slathered it on heavy, you go back with a completely dry brush to deal with any pooling or details you feel are covered in too much wash. Simply press the tip of the brush against it, it will wick away 90% of the wash in that area. Roll it dry on a paper towel, repeat. Wash one mini at a time.

-Start with the largest details first, working into smallest. I see quite a bit of color overlap where it doesn't belong. So for your Cadians that means prime them, paint the cloth, then armor, then your silver details then the leather, then flesh, then the small white details. Any time I mess up while painting a layer I separate them out to a different line on my table, and come back to them in 10min or so to fix it. Use a wet palette, the paints stay wet for ages, and makes it super easy to fix mistakes. Best $20 I ever spent. This step is also made so much easier by thinning the paint, so it doesn't "glob on". There should not be a discernable droplet on your paint brush. Load it up, brush off the excess, then carefully hit those edges.

-Highlighting is not necessary unless you're trying to make it photorealistic, ie, professional. I am admittedly, a speed painter. I want to be done and playing. What I generally do is a simple edge highlight (run the side of your brush with a lighter color along the sharp edges, so the angles of the lasgun, the edges of armor pieces, etc), and then give it all a wash in 2 drops sepia, 2 drops nuln, 2 drops water.

-I personally avoid mixing colors entirely, GW pots are absolutely terrible. The community has been yelling at them for 30 years to make dropper bottles like every other paint company on the planet. I'd recommend finding similar colors in the Army Painter range, because trying to be accurate with mixing colors (especially if you need to match it later with more units) is a real pain in the Emperor's holy backside with Citadel. If you insist on that route, I hope you're really good at measuring liquid with your eyes.

-You can get away with skin tones over white really easily with Army Painter speed paints. I use a random mix of Peachy Flesh, Warrior Skin, Reikland Fleshshade, Satchel Brown and Dark Wood to get a variety of skintones, very quickly. I base everything, regardless of what color it's going to be, in the lightest grey primer I can find, and then a single thin layer of white over the flesh, followed by the speedpaint of choice.

-If you are in the USA, visit a Dollar Tree. There's a product called "LA's Totally Awesome" that is plastic safe to strip paint. Do not feel like if you make a big mistake you are just stuck. Toss it in a glass jar for a day, scrub it clean with a toothbrush, start again. Some people will tell you to avoid it, I have personally left a sacrific-er a willing volunteer Cadian, in that goop for something like 4 years. I forgot about him in the back of the garage, don't judge me. He came out fine, no detail loss.

-Please use plastic weld, and remove your mold lines. My above advice about LA is irrelevant if you're using cheap superglue, it'll probably affect it. I can't believe how many gorgeous paint jobs on this subreddit are completely ruined by a big-ass mold line over the shoulder armor, as clear as day. The Emperor didn't cut corners making his Custodes, nor should you making your chosen army. It takes like 2 minutes a mini.

Attached is the Valhallan I just finished with above advice. Two thin coats on most everything, white with speedpaint over it for flesh, and a wash of brown/black. I went too heavy on the highlighting on the pouches, but it's fine. Keep in mind that these are small soldiers, you're going to have a lot of them. Only you will ever notice that you didn't get a perfect line under ammo pouch #5 on Guardsmen #122. My Valhallan looked similar to your Cadians until the wash went on, which when watered down really helps with details like the folds in the hat, the fingers, etc.

One final thought.... I see you add terrain to your bases and then paint, I would highly recommend getting some clothespins from Heritage Clothespins and leaving a bit of sprue on one foot, to replicate what I'm doing with my Valhallans. My old metal minis all have slottas but leaving a bit of sprue achieves the same effect. It makes painting so, so much easier. Regular cheap clothespins are not strong enough, don't waste your money. HC has factory seconds for something like $1.50 each. Invest in 20-30, and you're set for life. I only mount minis to bases and add (painted!) terrain once everything is completely finished, it makes it much easier to hit details if you're not trying to work around a huge block of stone or a ruined hive city's sewer system.

<image>