Learn English – How should this sentence be punctuated

Yes, it makes the most sense. But, for one reason or another, the written version doesn't tend to bother with any punctuation at all. The closest thing I can find to a definitive answer comes from the apparent source of this phrase. I don't know for certain, but I think it is extremely likely that this common phrase came from the song of the same name. As you can see in the link, the punctuation in the song's title is either "Home! Sweet home!" or "Home, sweet home". So, the way you want to parse the phrase at least agrees with the creator's intent.

I'd do something like

Dear xxx,

How are you doing with regard to

• sourcing the moose hair,
• reticulating the splines,
• extolling the virtues of silk underwear, and
• estimating the project completion time?

Basically, this just takes an ordinary list, punctuated as an ordinary list would be, and adds list bullets to aid readability. If you really wanted to, you could retain the colon after "with regard to", but I don't think it's necessary.

As with an ordinary list, if any of the list items contains a comma already, then replace the list-separator commas with semicolons:

How are you doing with regard to

• sourcing the moose hair, lamb tail, and armadillo feathers;
• reticulating the splines;
• extolling the virtues of silk underwear; and
• estimating the project completion time?