I suggest you get at least one thread chest (without the thread). I have the Sewmate IV and love it to keep sewing tools in such as the machine feet, scissors, etc. The drawer storage bin is great. The thread boxes were thrown in for free on my offer. I would not pay for them.
I love the outback extension for quilting large quilts. I pull my cabinet away from the wall and pull it up to do FMQ. I was sure I would not like the added height -- I don't like to be on a tall chair. I still use my dining room table to cut -- it's 29", the same as my cabinet. I'm 5'5" and it works the same as it has for the last 50 years of sewing.
When I get a sewing studio (LOL), I'll add a Koala craft table.
I have the front door shelves, but I really only use the one on my right. I'm not sure I would use them if I had the Quiltmate.
There are a lot of great brands to choose from. For me, the Koala was very attractive and has been wonderful.