No worries, have a special on baseboards till the end of May, 20% off if your looking for a 6' x 4' it would normally be €220 with legs special offer would be €176
The main consideration to building a helix is the radius, in 00 radius 3 is the minimum you should go. The smaller the radius the greater the incline so go as big as you can.
Try to keep the height between levels as low as possible.