spent most of last night laying awake. I get a bit like this when im 'on one' with something like this.
that's a good sign :)
its interesting and quite easy at the outset of any new design... in my experience though it gets harder the further you get into the nuts and bolts of the job... one small amendment can have a bitch of a knock on effect :(
its frustrating when you want to get building but try to design the knickers out of it before you commit because those amendments and knock on effects can be heart breaking if your half way through a build

having a Y axis that is longer than your X is pretty unconventional for obvious reasons... i can see your logic in expandability, if you will definitely expand if all works well i would keep the faith and go for glory at the outset on the proviso that the consensus was that your design would do what you required

iv not built a machine of that size but there are a few people on here that will give you a good idea if its doable 3m x 3m is quite a large machine... i'm not sure anyone has built one of that size on this forum ?

good luck getting to sleep lol