Marvel Chronology Project

I know Marvel Saga has new scenes which are incorperated into the characters chronologies. My question are:

To what point does the series go? In other words what Marvel event does it end with? I have 1-24 and not 25. and is the series narrated by anyone revealed at the end?, or is it more of an source book type of read?

There are 25 issues (I have all 25).
And it is the Watcher who is the narrator, of course. He appears on the very last page.

Is he watching this unfold from roughly 1985 or from an earlier time in Marvel history, and shouldn't he get a behind the scenes entry for 1-24 and an actual appearance in no.25?

Hard to pin down exactly.

The main retelling stops after the FF first encounter Galactus, and then there is a brief 3 page summary of events up to the death of Dark Phoenix and the Celestials judgment from approx. #300 of Thor. So it has to be after that point of time.

I would say he should have an actual appearance in #25

After the Galactus retelling, the book spent two pages doing capsule synopses of events that followed closely thereafter:

Thor's defeat of the Demon (JIM 124)
Namor regaining the Atlantean throne (TTA 74)
The end of the Hulk's servitude to the Leader (TTA 74/2)
Dr. Strange seeing Dormammu being trapped in another dimension by Eternity (ST 146/2)
Nick Fury capturing HYDRA's NYC headquarters (ST 140)
Daredevil defeating the Organizer and helping Ka-Zar regain his title (DD 12-14)
The Avengers's first meeting with the Swordsman (A 19-20)
Iron Man's first battle with the Titanium Man (TOS 69-72)
The X-Men's first run-in with Sentinels (UX 14-16)
Spider-Man's prolonged conflict with the "Master Planner," a.k.a. Dr. Octopus (ASM 33)

From there the book spent a page chronicling a number of universe-changing events from that point on up to T 300 when the Celestials judged humanity worthy of survival, then another where the Watcher delivers a closing monologue.