Gentlemen, this is a doddle in Designer. I produce such things all the time; set the job up as an A4 landscape, set up a guide at 148.5 cm, set up the borders and bleeds you need on each side, save it as 'Template' , open 'Template' and use 'Save as' to call it whatever you want. When you've finished each spread, save it, then Select All, then delete it; then 'Save As' and carry on with the next spread. I've attached a 4 page A5 brochure layout; for an 8 page you would have pages 8 and 1 for the outer, and pages 2 and 7 backing it up, then 6 and 3, then 4 and 5.
demo 4pp inner.afdesign
demo 4pp outer.afdesign