When checking rail fares look at splitting your ticket - look at national rail web site to see if your train stops at Stafford. If so it may be cheaper to buy 2 tickets - 1 from Manchester to Stafford & another from Stafford to Birmingham (you don't need to leave the train). It may or may not be cheaper
National express coaches might be a better option with luggage, albeit slower.
Many trains don't have much in the way of space for suitcases.