Hello from Cardiff!

[Jonathan]

What would you recommend as you guys know best? is the LC spindle really needed over a cheaper alternate such as the kress.

The Kress is in the end still a router, not a proper spindle. It will have more run-out, be noisier etc and won't last forever. The minimum rpm is 5000 ... whereas you can go lower with the water cooled spindle. That's good for cutting metals.
Maybe get a really really cheap router to start with then save up for the spindle? I started out with a router for about £6 from the car boot sale ... one of the ones from Aldi. This is what I have now got:

http://cgi.ebay.co.uk/2-2KW-WATER-CO...ht_7977wt_1139

For an A3 size machine the only reason to get the 2.2kW version is because it takes bigger collets. The extra power wont be required.

is 40mm Alu Profile ok to build a machine of my needs with?

Do you have a drawing of it, or better know its second moment of area?

is making the leap to 25mm supports really needed for a A3 machine?

It's not needed, but every little helps. The more rigid the machine is the faster you can cut whilst still maintaining a good finish. I regret not getting 25mm for the Y and Z axis, but then my machine is much bigger.

what Force Nema 23 motors will I get away with?

These 3Nm ones are popular/economical:

http://www.ebay.co.uk/itm/3-X-3Nm-St...#ht_1617wt_905

You could use less, but the price per Nm goes up if you do. The main thing is to look for motors with a low inductance and run them on a high voltage as that gets more torque at higher rpm. With those motors 70V will work well, which means you'll spend about £40-£50 on each driver.