As always it's all imho, and obviously it could be wrong way to do things.

Simple? Zenithal(black all over, grey 45 degree, white from the top) and ork flesh contrast for armor. Machanicus standard + administartum gray for rubber joints and gold of your choice for trims.

Complex? Black primer, Caliban green all over armor, lahmia medium + warpstone glow 2:1 - 3 layers on areas to highlight(AI already show you areas to highlight) each layer smaller then former by ~0,5-1mm depends how smooth you wanna transition to be.

Add moot green into the mix and more medium so it's 3:1:1 and continue to add layers.  If result isn't pop enough for you add some corax white in the end and highlights more. 

Mechanicus standard + administratum  for rubber. Gold of your choice.

Oh, most crucial part, you always should apply all highlights strokes from darkest part to brightest, or magic won't work. I mean literally move brush tip to center of highlight. Also stroke should be coaxial to brush  bristles. This way you get thinnest layer on start of stroke and thickest in the end. Like for shoulderpads you apply brom border to center. For gorget from shoulders to center, etc.

This is a great video showing how someone painted a green/black Space Marine very quickly to a very nice standard:

https://www.youtube.com/watch?v=ataC0VZDVx8

I have used this technique myself for different colors and can confirm - it works incredibly well. You will get miniatures that look about 10x better than you expect for the time it takes to paint them. 

Here are some Space Marines I just did with a steel/silver main color, using this exact technique:

https://bolterandchainsword.com/topic/385834-phandaals-completed-projects-necrons-space-marines-2026/#findComment-6151025

Highly recommend!

Your Green Templars caught my eye after reading that excellent short story you posted, about a Templar returned from the Deathwatch. I didn't comment there, so thought I'd make amends here by trying to help!

Greens tend to be quite forgiving in application, but the eye is very sensitive to variation there. I recommend keeping the base-coating as quick and simple as possible, so you can spend your time on the fun detailing stuff.

If you're after the effect of that first image (the warm, slightly metallic green with the helmet on), you could get a long way towards it by priming with Retributor Armour, then applying Ork Flesh Contrast over the top, avoiding the areas you want to remain gold like the pauldrons and right knee. That'll deal with the great bulk of your work in two steps, and keep things as smooth and consistent as possible. If you want the cooler green of the second image, try Terradon Turquoise over Retributor Armour.

The ever-excellent Chaosbunker has this extremely helpful article on using Contrasts over different paints, which included these images from GW Chelmsford. You can see the effect of various greens on the bases in the right-hand column:

If you want to see it on a marine, the example (not mine) through this link shows a Space Marine painted with Terradon Turquoise over Retributor Armour; which should give you a rough idea of how the cooler green would look.

Wow. I never thought of priming them gold. But if it's simple and it works, I'm all for it!

Thank you for reading my stuff and for the advice!

It honestly makes my day better.