Seat wise, it's tricky, but I think the limit tends to be if you are large enough that you can't fit in a standard seat with the arm rests down. I've noticed some airplanes now have arms that can't be raised all the way, so you can't lift the arm for more room. Leg room is a contentious one, because the airlines end up selling the space twice, once to the person in front, so they can recline, one to the person whose legs are in the space. I find that on long haul flights they make you put the seat up during takeoff and landing, and meal times, otherwise you're allowed to recline.
This is generally what I see too (frequent flyer, almost 100% domestic flights, between 2 and 5 hours in length. I am also a flier of size, and have never had a problem as I can sit with the armrests down (which I prefer as it keeps me from encroaching on the other seat) and the seat belt fastened without a problem.
I wouldn't attempt to bribe the flight attendants with chocolate. In all my flights I've never seen someone gifting the flight attendants to get better service. Definitely be polite and calm, even if trying to sort out a problem. If you want better service than the average flyer, book in business class, or fly often enough to get top frequent flyer points.
The only time I have seen this is a very frequent flyer who is on the same routes I take (I see him at least once a month-we are on a first name basis these days and ask about each other's pets). He brings cookies for the FAs. But he is also even more of a frequent flyer than I am (and I make a round trip about 40-45 times a year) and knows the FAs on our main route by name. And they know him.
Make sure your carryon is a reasonable size and shape. For the flight, I usually pack a sweater or jacket, for temperature changes, my Kindle for reading, a magazine for reading on takeoff and landing, tissues, mints and gum, a book of sudoku, and a set of disposable slippers/facemask/earplugs (obtained on a previous flight), and a couple of granola bars in case of flight delays. Don't check anything valuable - if you have jewelry, a laptop, a camera, etc, keep it with you.
These days some airlines let you use electronics during takeoff and landing, as long as they are in airplane mode. My main airline does. But you can't use a laptop (I assume due to size). Check and see what your airlines allows/requires.
For knitting - I'd make sure that you can take knitting needles on the flight, and that you can do the knitting completely within the bounds of the armrests. Having an elbow bobbing back and forth over the arm rest would be really annoying.
The only knitter I was ever annoyed with (and I have sat next to and near a lot of them) was one who used a lot of arm movement. She kept elbowing me as she clicked along. Other than that, it is a reasonable amount of noise (IMO) that is easily blocked by headphones. And I didn't find it too annoying, except when elbowed. :>
99.9% of flights and people on flights are just trying to deal with the pain in the backside that air travel is these days. In all of my flights, I have only ever really seen a small percentage of flyers who are truly obnoxious or blatantly rude. And have only been called back to the gate for bad behavior twice (once was a kid that would not settle into the seat for takeoff and one was a passenger who determined, after we left the gate, that he could not handle his fear of flying through the flight). Otherwise, most folks are, at most, a bit entitled and a bit oblivious to the fact that an airplane is shared space. I could tell stories about the entitlement of some passengers......
There are a huge number of folks who are willing to cut people a lot of slack for noisy kids, unaccompanied minors, passengers of size, bags that need a strongman to lift, kind of noisy/somewhat smelly snacks, assistance dogs that are scared to fly (yes-I sat next to the shivering golden retriever of doom one time-poor thing had never flown before and was just shaking the entire time) and people who are scared to fly (I sat next to the shivering teenager of doom once too-I think the golden retriever handled his fear better than the poor teenaged boy, who was also saddled with a couple of friends who were jerks about it).
Overall, as long as you are making an effort, most folks will make an effort and try to be nice about things. Because very few people really enjoy economy air travel these days, so playing nice with one another is the only thing that gets us all through.