you should definitely buy scrubs.
i think 11 players is what you need to ensure proper gameshape. if the total salary of your 3 players exceed the salary floor, then buy 1k scrubs. if it doenst exceed the salary floor, you can buy your 8 scrubs according to the difference.
for example salary floor: 70k, three players salaries total:46k (70-46)/8=3
then you could buy 8 scrubs all with 3k salaries.
buying higher salary players with better defences, you can reduce the risk of fouling out of scrubs, which could lead to gameshape problems.