Buying a SF i would focus on both the D's. OD and ID. Some say rebounding is also quite important but in lower leagues you can get by without having it. It really depends wat SF u want, a pass first in that case get a good passer. A scorer so get JS, JR and IS, DRV is also helpful. Most people have a outside SF with respectable in inside and vice verser. I think u may need to save more for a dominant all round SF for Div 4.
Shot blocking is good for raising salary but its debatable if u train it or not. Some say its underratted some say it raises salary, i train guards but if i did train big men i wouldn't train it. It might get a pop because its a secondary for most skills meaning training IS and ID the sublevel will go up. Some people only train it once a season though, really up to u
Hope that helps