Nice question.

1) Superman from Action Comics #1
Don't remember specifically--probably an early Superman Annual, around 1961.

2) Batman from Detective Comics #27
Probably Jules Feiffer's The Great Comic Book Heroes when it came out in 1965.

3) Spider-Man from Amazing Fantasy #15
Bought it new.

4) Fantastic Four #1
Bought it new.

5) Batman (new look) from Detective Comics #327
Bought it new.

6) Green Lantern/Green Arrow #76
Bought it new.

7) Superboy (and the LSH) from Adventure Comics #247
Gor a coverless copy from a friend a few months after it came out.

8) Avengers #4
Bought it new.

9) The Brave and the Bold #28
Bought it new.

10) Avengers #16
Missed it on the newsstand, but found a copy in the incinerator room of my college dorm right after I read #17 (to my great puzzlement.)

11) X-Men #1
Bought it new (the same day as Avengers #1, which came out that week as well)

12) Thor from Journey Into Mystery #83
Passed it over when it was new (didn't start buying Thor for a few months for some reason), and read it in its first reprint (Marvel Tales #1, 1964, maybe?)

13) Supergirl from Action Comics #252
Bought it new.

14) Captain America (origin story) from Captain America Comics #1
The Great Comic Book Heroes, 1965

Basically, with a very few exceptions, mostly 1962-64 Marvel and pre-1958 DC, probably amounting to fewer than 25 books, I read the whole Silver Age in real time, as it unfolded.
My real benefit from reprints was in Golden Age stuff. The Feiffer book, for instance, was a treasure which those of you who grew up on readily-available old reprints will have trouble appreciating.

Ah, the meek. Playing the long game.
Sneaky bastards.

--Denise Mina, Field of Blood