This is sort of a random question.
if you are on a tight budget, but want to expand the size of your machine (Mine from 500mm to 1000mm). Which direction would you expand first?
X or Y
I’m sure there are benefits for each but I’d like to see what everyone thinks about this.
Expanding Y would be easier. This is what I will be doing one of these days.
For the sake of around $40, I’d do both axes at once.
Having had to take my X-Carve apart a couple of times, the less often you have to do it the better.
That’s the nice thing about doing just Y. You don’t need to take both axes apart. 
For what I do, I only see a need for expanding one axis.
Expanding the Y axis would be more useful plus it’s easier to brace the extra length with brackets to the spoil board/extrusion which toy couldn’t do for the X axis.
Apart from the difficulty/expense of getting 1800mm Makerslide here in Oz, a bigger machine wouldn’t fit in my CNC shed!