The first thing of course would be understanding that all the things you are talking about in your theory book apply to a specific era of music that can only be used up till about 1900 or so. And the things you are reading are geared to help you understand the composers in those eras. I and V the tonic and dominant ruled these times and composers would never (or almost never) change keys without some sort of cadence I.E (V-I, IV-I, V-IV etc), what you have to understand from studying this type of theory is that the music is governed by leading tones, notes that by "nature" are unstable and literally lead to another note, if I’m in C Major the note B always leads to C, the note F always leads back to E. So this is why V goes to I etc. I believe that learning the fundamentals are essential because it gives you an understanding of where things came from. These basic fundamentals govern not just classical music but pop and rock music as well (I don’t say all, but allot of it, if not most of it). I mean look at Bob Marley, he probably never studied theory but yet all his songs are going I-IV I-V, this is because there is something physical going on in the harmonic series that makes such combinations sound good.
So understanding it means you don’t have to sit there messing around forever to stumble upon the same thing.
In Bachs time every note had an explanation, and if you ever had to write in the style of bach you're music too would have to have an explanation for every non chord tone. In other words if I am in G Major I dont just go C# Major, the two keys are too unrelated even though there’s actually nothing wrong with doing so. In bachs time it was wrong. If I want to however go from G major to say D major I can do so by creating a leading tone not normally in the key of G (F natural) F natural now becomes the leading tone to D major, and by creating a new chord G-B-D-F, I now have a V7 of V, G7 now leads me to my new key D major.
An Escape tone would be a non chord tone that skips in the opposite direction of the musical line
A suspention is a non chord tone that resolves on the next beat, If I have a 4-3 suspension, lets say im resolving a C chord, F would be a 4th up from C, which would reslove down to the third, so I would have C-F-G, C-G would hold over and F would go to E. You will see this happen over and over again. I can also have a 9-1 resolution From D-C in the same fasion,
Anyways I don't remember the others that you mentioned off hand (I have forgotten most of what I havent used) But i think the main thing to take from that book is a way analize music and understand what some of the greatest composers are doing. But bear in mind once you get to 20th century music this type of analysis no longer applys.
I am no way saying that this is the way to write or not to write music but it is critical to have an understanding. So keep it up!
People condone theroy and say it kills creativity. Most of the people who have said this to me have actually never studied. Also it is never too early nor too late to get started though like anything else the earlier the better.