Lack of head/foam/carbonation in my beer

You definitely just need to wait longer. I always wait at least two weeks, more for higher gravity beers. Waiting will not only improve the quality of the head and carbonation level, but almost everything else about the beer will get better if you give it more time.

A side note on your step 6, it's best to keep splashing to a minimum when racking after fermentation is complete. Pretty much the only time you want splashing is when transferring from the kettle to your fermenter on brew day, as you need to get oxygen into the wort so the yeast can get a healthy, vigorous fermentation going. Introducing oxygen after the yeast have done their thing can lead to oxidation and that wonderful wet cardboard taste / feel.

That said, oxidation can take a LONG time to show up in the flavor, so there's no need to be overly paranoid about it. It's mainly a concern with macrobrewed light lagers, where even the slightest fault is apparent because the beer itself has little to no flavor. I'm sure I've caused oxidation in my brews before, but they're usually too flavorful and consumed too quickly for the taste to appear. Keeping post-fermentation aeration to a minimum is just a good practice to follow in general, and especially if you're doing a big beer that will age a long time.

Carbonating the beer from priming sugar takes at least a week, often closer to 2 to be ready. The problem here is that you were sampling a too early:

After another couple of days I was tapping off nice pints of dark ale under reasonable pressure (at least I thought it was reasonable pressure - it might not have been) but with no head. I'd only tap a max of 4 pints a day for my wife and me... perhaps 6 tops.

After another 2 or 3 days I was beginning to get at least a thin layer of small bubbles sitting on top of the pint but nothing approaching a head, as such.

So you see after you've waiting a few days more the head is slowly improving. It will continue to improve over time.

Carbonation from priming sugar requires that both the yeast have fermented the sugar (taking up to a week for regular beers) plus that the CO₂ produced is then dissolved into the beer, which also takes a week or more.

Your next beer, a wheat, will have a better head, since wheat contains more protein, which contributes to the head formation. If you leave the beer at least a week before trying, ideally 2, then you'll get the head you're looking for.

Once you start drinking the beer, the amount of carbonation will decrease as the barrel empties, so you should get hold of the CO₂ bulbs to replenish the carbon dioxide in the barrel - it's there to push the beer out and to keep it carbonated.

As Denny mentioned, head formation is primarily related to protein though dissolved carbonation level will also have something to do with it. If you're adding a fixed amount of priming sugar to a single pressure vessel, as you dispense beer, the increased amount of headspace will allow some of the CO₂ to leave the beer, making it flatter.

You do not want to be "splashy" in step 6. Any time after fermentation has finished, you want to minimize the introduction of oxygen.

If your step 2 is a sort of "dry hopping", you'll want to do it after primary fermentation is complete.

Foam formation is related to the protein content of the beer and fermentation specifics. You can increase the protein content by steeping some non diastatic malt, like crystal, as part of your brewing liquor. Once you have the protein in your beer, increased hopping increases foam as the polyphenols in the hops bind the proteins in the beer. For the impact of yeast and fermentation on foam, see http://byo.com/stories/article/indices/35-head-retention/697-getting-good-beer-foam-techniques