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Sounds like you should have the basics, except for experience with analog circuits and analog design. You can find simple designs for analog buffers with level adjustment in the schematics for VCRs. The following comments are offered more for the benefit of other readers.
Composite video signal does not have to be bad. It is worth noting that the video terminal output of many professional analog camcorders was a composite signal. High end signal separators in monitors and other gear used comb filters to derive Y and C effectively. But those filters added cost. Often in home/consumer/modest cost equipment the separation was accomplished simply (and cheaply) by cutoff filtering at around 3 mHz with below 3 mHz for Y and above for C. These limits are inline with VHS recording capability and account in part for lack of S-VIDEO outputs on VHS gear. However, they are well below broadcast signal capability. (a bit over 4mHz for the NTSC Y signal component) and S-VHS, DVDs, STBs, and DV/MiniDV thus the addition of S-VIDEO outputs. Feeding a composite output from quality sources can look poor compared to S-VIDEO or component.
While digital is relatively tolerant of frequency response and linearity variations in the signal path, analog is not, A high frequency roll-off causes a loss in sharpness/resolution and non-linear amps cause gray scale distortions. That is where the multiburst, cable sweep and ramp signals come into play in testing/alignment.
Matching impedance is necessary to ensure video levels are correct (whites and blacks) are at the proper levels at the display. Within limits this can be compensated for with contrast and brightness controls on the viewing set but that becomes application specific and can reduce cross component compatibility of the recorded signal.
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