I measure my mix "parts" in dry volume, then hydrate as needed.
I would think a mix like that would be best suited for maybe some carnivorous plants like nepenthes. I would also use something like that for certain clones or seeds. I personally (in most scenarios at least) would leave out the verm, it's primary purpose would be to retain moisture, which the sphagnum does as well. Vermiculite tends to clog up my soil mixes, I uaually reserve it for top-layers when starting seeds, to keep humity high while under dome. In tht mix, the sphagnum holds moisture but is fluffy, and the perlite add more structure and air. Sphagnum is usually a lil acidic, if I remember correctly. Aside from that, no, that mix doesn't have much for nutes, it more about moisture and structure (which is why I'd use it temporarily, for seeds or clones, or carnivorous planta which don't want nutes in the soil)
I actually do not know how to get an accurate ph readin for soil... I know there's probes you can buy, but the cheap ones don't seem to read anything for me, and I haven't had te need to invest in anything spendy. I imagine you could test some runnoff water with litmus, but idk if that's really accurate.
I do know, where I used to live, if you had a plot of land you wanted to have tested, you could go out and dig up about a pints worth of earth (total) from like 10 different areas on that plot, mix it all together, and the university would analyze it for you tell you all about it- ph, loam:clay:ratios, mineral/metal content, probly a bunch more. And I don'teven think it cost, or if it did it wasn't much, maybe 100 bucks or something. Worth it if you're farming...