Question 1:
It depends. Set your amp to mid point on all the EQ knobs and adjust only the guitar settings. Repeat with the guitar settings in the mid point and adjust the amp. Which sounds better. There is not real right or wrong, but one of the two may have better sounding EQ.
Question 2:
On one of my amps, the presence control seems to boost the mid range. It makes the guitar stand out more in a mix of tone, like in a band. You can then hear it's presence, more that way. That's my theory, anyway.
Question 3:
If you are playing at low enough volumes that you hear the guitar acoustically over the top of the amp, you will get more off a combination of the two, rather than just the amplified sound. Headphones would help solve this, but to be honest, just adjust the volume of the amp up a little and you will hear your adjustments fine.
Question 4:
Yes, Get a pickguard. They even have clear ones, so no one will know !
. I don't hit my guitars with a pick, when I play, so it's not been a problem for me.
Questions 5 & 6:
The cheap ones are really just that. Cheap. The super high priced ones may not be worth it. Certain brand names come to mind that have higher prices , just because they can. I have started to like the cloth covered ones. Like this Kirlin 10 foot cable.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1 They don't tangle as easy as the rubbery ones, they look cool, and I don't get hum and the end covers have stayed on. It's around 12 bucks.
Question 7:
I have an older UltraSound amp, from before they were just made by Dean Markley. I would suggest one of those. If you can find them on the used market. However.... Just because your amp HAS those features, doesn't mean you have to turn them on. Leave them off and see. I think most acoustics sound nicer with a touch of reverb, so don't fear turning the knobs.