All good advice here. Have you researched long arm quilting on the internet or through your manufacturer. It always helps me to read all I can on methods. Do you have any opportunities to go to a quilt show with multiple
manufacters? Most tension issues are similar on all machines. Don't assume all problems are due to tension. As stated, go slow around curves. To get more mileage out of your practice pieces, use the same piece over again using a different color thread. And, try only one thing at a time to see if that is the issue before changing something else or it can get really confusing.
Maybe you can find a local longarm quilter who would walk you through all the steps and help resolve your issues.