Theoretical

It's largely unnecessary (and generously self-indulgent) to explain the concept of Compulsory Unit Selections to the B&C crowd. With his previous experiences in 3rd Edition Age of Sigmar (playing the big orks whose name escapes me - 'Ardboyz? Irongutz?), my opponent grasped the concept pretty quickly. Personally, I first learned Compulsories during my initial forays in Warhammer, playing Horus Heresy from 2015 until the first rendition's untimely demise (there's another conversation to be had elsewhere about the HH2.0 update and the loss of "the magic" that made that system appealing). We both enjoy playing around inside of tight boxes of rules, and I find that limitations and regulation breeds creativity, to a certain point.

At no point, however, have the 40k rules writers ever needed to convince Space Marine fans to take Tactical Squads - they're the in-universe and tabletop backbone of a Codex-Compliant Company (or Demi-Company), and a great hobby exercise - an opportunity to showcase the distilled essence and character of a Chapter. The colors, heraldry, and any weird quirks can be presented and not overwritten by duty-specific wargear or markings.

Practical

I committed to make the two identical Tactical Squads of my 1,000pt list the first units I completed in the project. Tactical Squads Andreus and Mattean are 5th Company's 1st and 2nd Squads, and in 5-man form, both armed with a Plasma Gun. The Sergeants are armed with Power Swords (denoting induction into the Velocitari), wear laurel wreaths (denoting secular rank and the stewardship of a particular shrine on the Company's Charge-World), and each wear a copy of the Lectio Divinitatus on their hip. Their tilt-shelds display the 5th Company's battle-heraldry, a simple-to-freehand red stripe on a grey field. I tried to add some sort of gubbin or bit to each Marine - a purity seal there, ammo and grenade pouches here, etc - just to add some interest to the units.

Painting itself was a pretty straightforward tried-and-true method. For the undercoat, a tricolor zenithal + purple wash + drybrush, to create shadows, add depth to recesses, and strengthen highlighted areas without any sort of cerebral labor. After that, I added colors (sometimes all at once, sometimes progressively layering) with speed paint. The lack of any sort of finesse will show to the trained eye at 2" away, but I'm at a stage in the hobby where I really don't mind okay-painted minis, so long as I get to roll dice and make pew-pew noises.