I'm in the learning/pre-planning stage and am trying to get my head round what to buy for my first machine.

I know everything will make more sense to me once I've got my hands on a machine (or better yet the parts to build one) because that's how my mind works. But I'm hesitant to buy something so small or cheap it's useless or to invest much in a decent small build which would eat into the budget for a potential 'proper' build later when I think I'm starting to understand how all the bits fit together. All things considered the best option seems to be trying to plan the build I really want blind.

Based on the idea you should always go bigger than you think you need I'm looking at a working area of 400x200x200mm and will be using the machining friendly aluminium.

I have fallen at the first hurdle though as I'm not sure whether to go for a 200mm moving gantry or a 400mm fixed gantry with a moving bed. When reading moving bed is only recommended for 'small' machines but that's relative - compared to the door size monsters some people make I would say this classifies as small, but 400mm is more than half a door so maybe it's not so small?

I'm thinking moving bed would be easier/cheaper but would like to give someone with experience the chance to say that it's not much harder (or maybe easier as it's so small?) to create a rigid 200mm moving gantry than a 400mm static one, not least because this would make the machine significantly smaller.

Thanks in advance for any thoughts.