Yes Its a modular system. Once you have a 4X5" setup you can change to a 5X7 back and bellows keeping the front. Next step is a 8X10" back (and bellows for that.)
I have a 5X7 Norma and a 4X5 reducing back. I wouldn't call it leight though since mine in 5X7 setup incl a 150mm ( just covers 13X18cm) weigh more than 5kg. Great camera though and I look forward to use it more.