Hello,
I'm sure everyone is already tired of all the beginner questions, but I didn't find an answer to this one.

I've designed my first CNC mill, which is supposed to be mainly out of metal.
I have tried to use mostly off-the-shelf components such as aluminium profiles and square aluminium pieces, but there are some custom shapes.
As of yet, I do not own a mill, just the most basic tools such as a grinder and a drill press.
Wouldn't it be sufficient to just cut these custom pieces out with a grinder, make them as flat and accurate as possible (with my tools), assemble it and machine a plywood or MDF bed flat to then machine these pieces with this temporary setup?
As I understand it, the imperfections of the machine are relative to the workpiece/bed, so if you were to machine the bed itself flat, the pieces should be accurate enough.
Am I correct in my assumption, and what other possibilities would I have if I were wrong (without spending thousands on an actual mill just to manufacture parts for a CNC mill)?