Theres more than one "bill starr" 5x5. You have to clarify. But I take it your talking the advanced "DFT" 5x5, i.e. the first program listed in the sticky, so you would be working up with ramped sets to a 5 rep set that was heavier than the Monday sets across.
I would expect something at least 20 pounds heavier for that depending on what the ramp up sets are and how close they are together. It is possible, I would expect to see up to 30 pounds difference there. I just took a look at 0311's old journal and his first week was a 30 pound difference so I'm probably right about that but it's hard to predict the difference between sets accross and ramped sets for anyone individual especially considering that the work up sets effect your final 1x5.
So 5x5 is 5 sets of 5 reps with working set weight (warm up to the target weight for the week and proceed through 5x5 with that weight). Where 1x5 is present you are pyramiding the weights upward each set to a target set weight for a single set of 5 (it's still 5x5 but each set gets heavier and your target set is the top set of 5).
It will be best to start conservatively...lighter rather than heavier and the Monday and Friday are two different progressions. They have two different target weights and are not to be thought of as tied togther in any way.