same here, i try to keep under 8ft. whenever possible but feel more comfortable under 6ft. Have done a runs close to 20ft, but huge risk of expensive failure.
friction/tension is your enemy: overlaminate hanging off the edge that would drag/stick to machine as it cuts, material that is not squarely loaded, or front/back material coiled on itself adding tension to the feed of the machine ....will gradually tug your media off-track as it feeds forward/backward repeatedly.
I think the longest run for me has been about 15ft, more or less. these aren't my favorite as they took some time getting used to.
What I've gotten our team to do is to make sure they trim off the excess lam hanging off the edge as I've had jobs not even wanting to run because of these (almost gave up, noticed lam, trimmed it off, cut perfectly, now is a norm for us)
I don't use a take up or put anything on a roll as I've noticed I'll get more errors this way so I just let it all hang. Don't think I've had any issues with this.
As for loading it squarely, I've noticed with longer print and cut jobs, even if I try to get it on the printers take up reel all nice, it takes up all crooked... so when I put it on the cutter, the material isn't square and the plotter can't read the reg marks. Sooo.. other norm is to draw little tick marks at the edge of the material that lines up with the horizontal line of the crop mark. I use this to load the material square (we used to use a ruler or estimate that it's straight... not anymore!). If it still doesn't read, I watch how the material runs through and if it swings left or right a certain amount, I load the material, swinging it clockwise or counter-clockwise that difference. Run it again and the material is now "square"
If it's print and cut lettering, I make sure to go in Flexi and change the cut order so it starts at the "bottom" of the print and makes its way up without jumping from a random letter or shape in the middle of the print and going back down. Takes time but is definitely worth it to make sure it's not going to jump around and feed all crazy and then your letters get all wonky.