Welcome. You found a great resource for answering questions and discussing all things homebrew. And about 70% of the info is accurate. =c) But these threads go back many years and just about every mistake one can make has been discussed and documented at some point.
Wow. Not disappointed.
This set-up is great but mostly duplicative for me. I will let someone else closer by and in more need of a full system (at a steal of a price) claim this.
Newer brewer weighing taking the next step-up - this is your shot. =c)
I used those fermenters several times with yeast, trub and such but up to near the spigot. It still worked fine in my experience. You could also just use a siphon if the spigot does get jammed.
To answer your later question, no it will not have a noticeable effect. Corn sugar would raise ABV and thin out the beer a little bit. But most people would never notice the difference (and half the people who did would probably prefer it).
I've done this several ways, and I actually liked the cold steep overnight method the best and it yielded the best results. Your mileage may vary.
Alternatively, mashing the base grains first, and then removing and mashing the rest in a bag was my second favorite option.
Third, replace some...