The impedance is not usually an issue if it is high enough – Eclipse is 150K, which is higher than many. Don't think there is a meaningful concept of "impedance matching" with a guitar. But, note that the tone will vary with lower impedances – this you have to judge for yourself. As I understand it, the Eleven rack changes its impedance to simulate various vintage pedals – you have to judge whether this is valuable to you. Digidesign says "There's no right or wrong way to do this, experiment until you feel like
you have a configuration that sounds and feels right!" I would concur – these things are very subjective and I can't know what would please you.
Nothing in the chain will increase quality (as defined by the absence of bad things). But, some effects may make it sound better (to your ears) – this is not the same thing.
The order of effects is important – but it depends on what you are trying to achieve – beyond this Forum to advise on such.
The 7600 and 8000 have slightly better analog circuitry than Eclipse, but this is unlikely to be noticeable in guitar applications.