I have the Avante/Crown Jewel on a 12 ft table. I upgraded from the 16" HQ which I bought used. I had that machine for 8 years and maintenance consisted of removing lint in the bobbin area and adding a drop of oil with every bobbin change.
The Babylock dealer in my area is selling "Quilt Motion" as the computer software. Friends with Quilt Motion hate it as there is no support. My system has "ProStitcher" and it has a lot more capability than Quilt Motion. HQ has a ton of videos on how to use the machine and the software plus there are live webinars every other month. Go to the HQ website and look at the "education" tab.
The tables sold by Babylock and HQ are different so take a close look. Babylock's are by the Grace Company and look like the wooden frames Grace Company has made for years. I prefer the smoother look and feel of the HQ frame but each to their own.
I use all types of thread and am constantly changing the tension. Jamie Wallen does a great YouTube video on tension that is applicable to all longarms (Taking the stress out of Longarm tension). Let your dealer know tension is an issue for you and have them show you how to make changes. Or you can stick to a particular brand of thread and the same type of fabric to avoid most of the tension issues.
Like any other tool, you need to practice and develop your confidence level as you build your skill set. Don't expect to learn everything overnight and don't be over-critical of yourself in the process. This is a big investment so take your time and if possible, test drive other brands.