You've summed up the situation well.
This is an area in which I have done a great deal of research, so I will respond from that perspective.
I don't know which book you have, but one must always remember that this is a scientific hobby (whether we like it or not...note the line below my signature
) which means that knowledge will always be increasing and things will change accordingly. When I started in this hobby, no one did water changes; now no one will tell you not to. We learn.
While the internet has given us all more information, it is not always reliable. Anyone can set up a website, or write articles in Wikipedia. The benefit of a forum is critical analysis by other members, much like the scientific community at a less advanced level but none the less extremely beneficial one. And there is the matter of the source; who authored this or that is highly significant as a guide to its reliability. I could tell you that cardinal tetra must be kept in very soft acidic water; so what? I'm not a biologist. But when Dr. Jacques Gery, Dr. Stanley Weitzman, and similar write this, you can accept it as absolute scientific fact.
We have a profiles section, second tab from the left in the blue bar across the top. Many fish and plants are now included. Most of the profiles were written by me, and the data is my summation of a number of sources that have a high degree of reliability. When I come across varying opinion from equally reliable sources, which does sometimes happen, I give both views and indicate it. The information in the profiles is not mine, but it is well documented.
To some specifics you raise. Hardness (GH) and pH are important, very much so--but in context. Varying pH can kill fish. Hard water will shorten the lifespan of most soft water fish. This post will become a novel if I digress into this, so I won't at this time. Spawning is one of several indicators; if soft water fish won't spawn, it means the water is clearly having some effect on their physiology. And wild caught fish do have a much greater problem with this. If nature has taken thousands if not millions of years to develop a species, we shouldn't expect to change that overnight.
Your hardness numbers are good, and in an established aquarium the pH will lower naturally. There are ways to assist this initially, we can discuss later. My point here is that what you have out of the tap is not prohibitive.
To your SE Asian plans: Below is a photo of my former SE Asian biotope, which is one example; this was meant to replicate a shallow lagoon, using a 29g. The second photo is a very similar setup in my 33g. I would avoid dwarf gourami, the problems are set out in our profile. [By the way, if the name is given the same in posts as in the profile it will shade, as it did here, and you can click that to pop up the profile.
] Sparkling gourami (pygmy) are fine, a small group is best, say 2 males/3 females or 5 if unable to tell. You don't want Zebra Danio in with gourami; the danio are active swimmers, gourami are sedate cruisers. Rasbora are good with gourami. In addition to the Trigonostigma species (the Harlequin Rasbora, or the even nicer Lambchop Rasbora or better still the Hengels Rasbora
), there are those in Boraras (Dwarf Rasbora, Mosquito Rasbora). The Eyespot Rasbora (Brevibora dorsiocellata, likely your Emerald Eye) is another, I have a shoal of these in my 90g with some Hengels. Dwarf loach is fine, active but in my experience (I've had these for years) not a problem. The similarly-sized Dwarf Banded Loach is very nice too, I have both of these in my 33g. In the tank photo below, along with all these I had two species of Chocolate Gourami. A highly sensitive fish, and one that absolutely needs soft water.