Everything that you are experiencing, so have I. But time and practice has helped me tremendously. The art of practicing is the key. I remember 25 years ago when I started crocheting, someone told me that you should crochet for a few minutes, take it out and start again because whenever you start a project, you are not relaxed but after a few minutes you begin to relax and all is well.
I believe that my saving grace was to slow down. I was trying to fmq faster than my hands and brain could comprehend. (I always start out too fast.) After I get myself relaxed and I slow down everything falls into place. As my husband would say to me, "You are not killing snakes!" I still have a problem with "shifting". Conquering this problem is, again, to think about what you are doing when you are doing it and double check that the needle will reinsert where you want it to. As far as different length stitches, that still plagues me, however, when I slow down it gets much better. I have to tell myself (every time I start fmq) not to think about the WHOLE project, not to fuss about how much more there is to do - I have to just concentrate on the small section that I am working on and eventually, it will be the last section.
"Gloves or not to gloves" that is the question. I started out with store bought quilting gloves, but did not like having to remove them and put them back on. In a online class that I took from Craftsy, I learned to use small squares (3") of the rubbery stuff you use under rugs. I keep a whole box of them next to my machine. They work beautifully. All you need is a little grip.
The Craftsy class that I took is called, "Quilting Big Projects on a Small Machine". It is a great class and you can refer to it, literally, forever. Once you buy it, it is yours to keep using. You can ask the teacher questions and she gets right back to you. I learned so much from this class that it shocked me as I must have 8 or 10 FMQ books. I followed her directions and sailed through a double-size quilt like a breeze. Perfect? No! But I have so much more confidence now that I look forward to the process of FMQ and love to know that, "I can do it!". Good luck. Let us know how you manage after all of the Boards great tips. Yolanda Wood River