Doesn't the squats say 2x15 or 3x10.... Which are you doing to = 12,12,12,8?I was under the impression that it would look something like (for 3x10) Yx10, Yx10, Yx8, more is say Yx6....
Next time Yx10, Yx10, Yx10...then up weight....
Yx10, Yx9, Yx8, more Yx5..
Yx10,Yx10,Yx10.....Up weight Etc...
The head isn't meant to face down, just so the back is straight. Shoulders should be so tight that head nearly sits in correct spot without thinking.
Also, if you're doing a 5x5 deadlift day as well, you aren't doing his beginners program anymore, as it strays from it? Not that it probably matters, unless it's what's slowing progression.
Definitely get yourself some 1.25kg plates.
If you're grinding out an extra rep 3xweek then going up 2.5kg a week, in 52weeks that's a lot of change.