On the navy blazer: I stand by including it as a necessity. Wearing a navy suit jacket isn't completely horrible, but I think the navy blazer represents a major improvement. To me a suit jacket worn as a blazer sticks out as exactly what it is. I know that outside of SF people don't realize that consciously, but I think they notice it as something not quite right. As an added advantage, you don't then need to worry about differential wear between your suit jacket and trousers, and you don't need to worry about ruining a whole suit if you ruin the suit jacket.
I think there are plenty of occasions where a blazer is appropriate but no jacket would be too informal and a suit too formal. Some holiday parties. Many "business casual" events. Going to dinner with your girlfriend's parents for the first time. A matinee at the opera or theater (Yes I know people wear shorts to these things but c'mon, have some class). Et cetera.
On the reppe tie: I don't think it's the only good choice, but it's a good choice for a tie to go with your blazer, for an American. I should have made that clear. A neat was suggested, but some (including Manton) find this too formal for a blazer. I wear neats with odd jackets all the time and don't really mind it, but a neat is a bit more formal than a stripe. For people on the level that this list is pitched to, it doesn't matter that much, but why eff with it? A knit is a decent answer too, but it's a little bit "fashiony" in that you don't see one every day. A reppe stripe is, from an American point of view, very much playing it safe and a classic choice to go with a navy blazer. It looks a bit collegiate maybe, but it's never in poor taste, provided you have any sense at all in the colors you pick. As far as the suggestion of a wedding tie, 1) that's already my suggestion to go with the navy suit 2) wedding tie is too formal for a blazer IMHO.
On shoes: black cap toes aren't ideal for a blazer. But it's not terrible. I'd rather wear black cap toes with a blazer than a suit jacket wear a blazer should be. Remember, we're talking bare necessities. If we could convince this person that they could wear a nice pair of brown derbies or loafers for much of their non-coat-and-tie situations as well, and that the investment in a second pair of shoes is therefore worth it, then I'm very much in favor. But shoes are expensive, and supposing that sale couldn't be made, they would not look like a doofus if they only had black shoes. At least they won't be duck-billed rubber soled loafers.