Disclaimer: I'm a prawn.
That said, you bring up a valid dilemma. Advertising on the first book when it's released gets no sell-through. Advertising on a later book only works for people who read the first book--but if you don't advertise the first book initially, who exactly is it that would have read that first book? Also, a lot of promoters won't feature anything except the first book.
Perhaps the ideal if one had the patience would be to wait until the first three books were ready and then release all three more or less at the same time. I'm not sure if this is still true, but it used to be that the new release period was the easiest time to raise rankings (and hence the best time to advertise because advertising produced more impact than at any other time). Anyway, with three books out at once, you can get the benefit of early advertising on book 1 and have sell-through.
Failing that--and I'd never had the patience--a slow build is probably best. That means doing some advertising on book 1 when it comes out. You may lose money, as you point out, but these days sales without advertising are going to be few and far between. When subsequent books come out, no one will have read the first one. Also, you don't have any way in that scenario of building tools like a mailing list, which many people say is highly desirable for building sales in the future. Of course, you can mitigate that effect to some extent by running promos on the first book each time you release a new one. You get sales on book 1 and some sell-through. Also, some promoters might run more than one book in the same month. Not so long ago, I released a book 2 and promoted both 1 and 2. Almost every promoter was willing to take book 2 if they were also promoting book 1 within the same month or so.
Slow builds are just that--slow. However, over time people who started out as social media followers or mailing list subscribers can turn into genuine fans who might actually buy something. That does mean having a flow of new content coming to satisfy your audience.