17 hours to build a Makerfarm I3v - a month to figure out how to tweak it - 4 hours to build a simple sounds like a breeze.
I think I will buck the trend a little and say go for the assembled unit unless you are very mechanically inclined and certain that you can get it done without any problems. Once everything is assembled, whether by you or someone else, when you begin printing there will be things to tweak and level and align. If you are not positive you did the assembly correctly you will always have that in the back of your mind. If mechanical assembly is new to you and 3D printing is new to you then when you have an issue you won’t know which of these new skills is at fault. After you have been printing for a while, you can always print the parts for a new machine with a larger build area.