You will not regret getting a servo motor! I used to absolutely dread sewing with my industrial machine for the same reasons you stated. The thing was either full stop, or full speed!
No, the duct tape does not stand up, you just stick a hunk on the bed of your machine to use as a visual aid. If you want a 1/2" seam allowance you place the tape 1/2" away from where the needle goes through the bed of the machine, etc. After a short time, you'll be able to just eyeball the proper distance from the needle to the edge of your work.
My suggestion to you is to practice, practice and more practice using scrap or heavy fabrics, such as heavy canvas or go buy some really cheap, heavy upholstery fabric, or ugly vinyl off the clearance table at your local fabric store. Practice sewing straight seams. Then when you get the feel for that, practice curves going both directions. Practice sewing with one hand, while holding down the manual reverse button with the other (back stitching). Also, if you get a servo motor, practice starting and stopping the machine exactly where you want it, with the needle in the down position, through your fabric/leather. That way, if you lift the foot, the fabric won't accidentally come out from under the needle, and your seams will remain neater looking. Learn to use the knee lift, but do NOT rest your leg against it while sewing.
You'll learn much quicker than you think you can, but you will need to work at it a bit. Most of all quit holding your breath! RELAX and enjoy your learning experience. Laugh at your mistakes. Learn from them. Take your time, when you feel anxious, stop, get up, and go get a glass of water, or just take a break. Take time to think about it, and then go back and sew a little more. Before you know it, you'll sew like a pro!
Okay, I'll shut up now and let you go ogle the servo motors