Do I need to take a couple of shots to manually figure out the exposure in M mode by reading the meta info of the pictures taken?
Well, you may need to take more than one shot, so you can see how the flash behaves, adjust settings, and reshoot. But with TTL, you may not need to.
Basically, unlike ambient-only exposure, where there's a single exposure level that works as a "good" exposure with flash, there is any combination of ambient exposure and flash exposure that can work from having a black background and all-flash lit scene to a fill-flash scenario where most of the exposure comes from the ambient and only a little from the flash.
Your meter, in M, as you've noted, is only good for setting the ambient exposure, not the flash. But TTL is going to do what you want: put the flash into the scene to meter the flash, and adjust the flash power to what the auto-exposure system thinks is good.
So setting your aperture and shutter speed is mostly to set your ambient level. If you want to kill the ambient, you'd set it to something like -4EV or -5EV. If you want fill flash, you'd set it to something very close to where you would if you were only using ambient light (the meter needle near 0). And if you want to slightly underexpose the ambient so the flash-lit bits of the scene "pop", you set to -1EV or -2EV (or however much you'd like).
You then take the shot. Hopefully, TTL got you what you want. But if it didn't, then you can use flash exposure compensation to adjust the flash power, or exposure compensation to adjust both the ambient and flash exposure together. You can judge the exposure from the shot taken by looking at the histogram and the thumbnail image together (no need to go EXIF diving). If you are using M on the flash instead of TTL, you basically have to make a judgement call on where to start (or you can just try 1/8 or 1/16 power, which are the middle settings of the 1 to 1/128 power range), and adjust from there.
Keep in mind that while ambient exposure is controlled by iso, aperture, and shutter speed; flash exposure is controlled by iso, aperture, flash power setting, and flash-to-subject distance. If you need a brighter ambient but the flash level is fine, use a slower shutter speed or increase the iso/aperture, but adjust the flash power (or hope TTL does it for you). If you need a brighter flash level, but you want the ambient to stay the same, you can increase the flash power, move the flash closer to the subject, or increase the iso/aperture and compensate with a faster shutter speed (assuming you're still within your sync speed; being above your sync speed and using HSS can require more flash power).