Not an expert nor an O+G player, but 30 orcs and 40-50 goblins is a fine unit size. You'll get some use out of the 8th-ed Horde formation, especially with night goblins.
In general, things are more mobile and charge farther (but randomly), forests restrict your movement less, close combat is full of more carnage (but a little less running away). I only played about a year of 7th, and I like 8th :)