You have to have made 10 posts to the forum before you can upload pictures but you're past that already. You may also have to reduce the file size. I generally reduce pictures to about 800 pixels wide for this purpose.

Re a second ballscrew: I've never used a machine with only one so can't really say how significant the performance difference is. Only you can decide if you want to spend the extra cash and the time waiting for it to arrive or whether to build the best machine you can with what you already have. You still have more parts to buy anyway and a design that allows for a future upgrade is not impossible with some thought.

Kit