I thought about going that route, but when I started to consider shipping on some of the upgrades later, I changed my mind and ordered them with the mill. It saved me hundreds, if not a thousand. Items like the rotary table would be trucked......not cheap from Toronto to Oregon.
I also didn't want to have to have the machine down later or have to deal with the work. If ordered with the machine, they do all the installation. It did make for a good bit more money upfront, but will save me a lot later.