12/8, key of F

I am trying to work out the chord progression while trying to learn about the concept of secondary dominants. (BTW, I have minimal keyboard skills--I'm figuring this out on bass).

I've been told that a II7 is frequently used in the first ending turnaround as it seems to be here (V7 of V, right?). But would the II7 in bars 3 and 4 of the verse be considered a secondary dominant?

Also, does the key signature change to Bb for the bridge (since there is an Eb in Cm7 and F7, or does it stay in "F"? If the key indeed changes to Bb, then the Cm7 is the ii7; but if it stays in F, then how would one characterize the Cm7?

Here is what I have (minus the walkdowns):

Intro:
F -- D7 --G7 -- C7

Verse:
F, E --F -- G7 --G7
Gm7 -- C7 --
first ending: F, F#dim --G7,C7
second ending: F,Eb--F

Bridge:
Cm7 -- F7 --Bb --Bb
G7 -- G7 -- C7 --C7

Any corrections or thoughts re secondary dominants are welcome. Thanks.

Interesting questions.

In traditional theory, a II major chord would be considered a secondary dominant. Since the ii chord is minor when derived from a diatonic scale, a II major's function is usually as a secondary dominant. (but note in the verse that it does go to the minor before going to the V) By this reasoning, the D7 in the intro would also be a secondary dominant. It is VI7 -- the V7 of II. This creates a cycle of 5ths, all major, one secondary dominant leading to another.

In the bridge, you could say that a temporary modulation happened. Cm7 - F - Bb is a ii -V - I into the key of Bb. But then right away it works it's way back to F. It doesn't stay in Bb long enough to really be considered a modulation, IMO. So the Cm could be thought of as v or "5minor".

Popular music fake books and lead sheets take a more liberal approach to theory. Chords like II7 or v(minor) are freely used without fully considering their tradional harmonic functions. Jazz and popular songs are full of temporary modulations and 5th-cycle progressions. We've become used to hearing chords of most any type built on every degree of the scale without them serving a "traditional harmony" function. What establishes a real, full modulation is somewhat subjective, but I think that it's when a new tonic is established, and then a progression develops and returns to that tonic.

In Nashville we use a shorthand of numbers to make charts. All numbers are considered major unless otherwise indicated. Here's "So Wrong" in Nashville Numbers:

Intro:
1 67 27 57

Verse:
1 7 1 1
27 27 27 27
2-7 2-7 57 57
1 #1dim. 2-7 57

...etc.

At the bridge it would be:

5-7 5-7 1 1
4 4 4 4 ...etc

This is like a hillbilly version of figured bass :)

how does the nashville number system deal with key changes?