Although Vanguard's "Small" Cap fund has a lower expense ratio, it's mostly mid-cap stocks (59% according to Morningstar data). Since Northern Trust's Small Cap fund holds 23% mid-caps (the rest small/micro), it's actually a better small cap fund, in my view. Despite the higher expense ratio (0.08% vs 0.05%).
Your allocations seem fine. You might want to read up on small cap performance. Small caps don't always outperform, so you need to be prepared to weather the times when that happens. Reinforcing your views may help. Larry Swedroe favors small cap value stocks, so you could read one of his books.