New CNC Mill on the horizon

[JAZZCNC]

As for the main material lets assume I use aluminium flat bar, how thick and wide does this need to be given I plan on using t nuts to secure down any spoil board or at least some similar sort of system.

On my Old machine I used similair setup with approx 35 x 16mm strips but I'd suggest thicker material 20mm min depending on support spacing.
Now this worked OK but in all honesty I found it to be mostly waste of money as 2/3rds was covered with some kind of spoil board which meant couldn't access T-sots so material was screwed down etc.
The area that wasn't covered was only used when I needed better accurecy on say things like engraving etc and I didn't want to surface the whole bed.

The type of work your mostly doing will determine which suits best but I found that while mostly cutting aluminium and mostly 2D profiling that a Good stable spoil board with a Matrix of holes using threaded inserts worked best. It gave good clamping options and most flexabilty for work fastening.
Very rarely did I need to remove the spoil board for acceess to more accurate aluminium base.

If you need accurecy but not over a large area then I'd suggest buying piece of Machine tooling plate and drilling matrix of holes. Then cover rest of bed with stable spoil board material and use T-slot track or Matrix of holes again.!

Just T-slots I find restrictive when using as general all-round machine cutting mixture of materials and Job types.!!