Sign or don't sign on every page depends on the lawyer, the signing is just to safe guard both the seller side and the buyer side, that you the buyer read and acknowledge to the terms and condition, normally they will request buyer to sign at special phrase if the SPA is different from norm.
But if you look from another side, if you don't sign, if there is changes to the SPA, buyer can also hire lawyer to fight for them... it works both way.

Full deposit is required upon signing the SPA, it is mentioned in it