Gary,
After reading this forum for a while and having experimented with wooden framed and now a steel framed router I can't help thinking that the most practical and the cheapest way to achieve what you want is to build two separate machines. Do you really need to cut 1m sq lumps of aluminium to .02mm accuracy? I assume not, but building a machine that can will cost you big time if that's what you need.

However, a small, fixed gantry machine that can cut smaller pieces of metal with that accuracy would be way simpler and cheaper as would a wood-only moving gantry machine with the bigger footprint.

The key piece of 'analysis' required to relieve your 'paralysis' is "What is the largest piece of aluminum I need to cut to the finest tolerance?"

Kit