New Boy introduction

[Crunch]

I have a few questions, if this is not the right place to ask please advise where to post.

What is an acceptable weight of a gantry with every thing on it including spindle, it terms of performance, I understand the heavier it gets the more effort it takes to start and stop it when moving due to the mass. Do you just deal with the extra weight with gearing or bigger steppers? Or is there a sweet spot in weight ?

I'm not 100% sure on how the axis are, as some machine I've seen shows front to back as x axis and others machines x axis is left to right.

Also which ball screws would be best to use,
2 x 900mm 1605 or 1610 with pulleys y axis. ( front to back ) or
2 x 900mm 2005 or 2010 with pulleys y axis. ( front to back ) would you get whip on this length and would these be better with a heavier gantry?
1 x 1200mm 2005 or 2010 with pulleys on x axis ( left to right ) again for whip due to length .
I've based axis direction on most machine I've seen are this way, but there are many that show they are the other way.
Which is correct ?
Do you know why different machines show different ways ?

Regards Paul