My 1st Hybrid Steel/Ally (1150 x 850 work area) (comments/advice please)

[EddyCurrent]

I'll also increase the distance between the blocks as suggested. [I]What should I look at for a minimum please?

Well mine have a gap of 95mm, that is inner face to inner face, I calculated that as the best for my machine.

With regard to the bed, I urge you to use birch plywood rather than MDF. I used two layers of 19mm and sealed it all with a 50/50 mix of polyurethane varnish and danish oil. That's after leveling the bed by running some G code to run the router over it with a large end mill cutter.

With regard to aluminium, I thought I might do some cutting of this myself but when you consider the requirements for lubrication/coolant, a wood cutting router just does not have the appropriate bed arrangement.
You might want to think about that in your design before starting the build i.e. an aluminium T slot bed might be a better alternative.