Okay you want to build an all round Gantry router to cut up to aluminium. Lower your bed and re-enforce it as suggested though don't over do it too much (we DIY folks do tend to over build). I would strongly, strongly suggest putting the Y axis screw behind the gantry beam if at all possible. it reduces issues with swarf and makes lubricating it much, much easier.

Go looking through the build logs as I know there is some very good designs there. You don't have to use any of them but they do give a very good head start. Also I don't see allowances for cable paths; that is something you really want to think about now. later it will bite your back side and cause issues (I can think of a few members who can tell about the headaches of wiring gone wrong).

Jonathan is correct that at that length 1610 will do you well and you can always work with the pulleys to get the resolution you want.

Good luck and keep asking questions.

Jonathan, Gecko are good equipment and they stand behind their warranty as more then a few folks have proven. Yes, they are a bit costly but they are serious kit for some one wanting a business level ROI (return on Investment). Next you will be telling me my Leadshine AM882's are over kill. Horses for courses.

-Michael

PS Contrary to my long absence I have not died nor fallen off the face of the earth just been very very busy.