Johnson has not signed many players so far because he has been waiting for the John Stones to Chelsea/Man Utd deal to go through. If Stones does go for the rumoured fee along with the Holgate deal Johnson won't have to settle for his original targets and can look at signing players like O'Sullivan and Pearson.
He has also said that it may take three transfer windows to get the squad together he wants for the upwards drive. That might similarly include the additional income. Hope so.
Trouble with that is any players he signs that are any good will soon be gone. We rarely keep a very good player longer than a season (Hourihane appears to be an exception, but he has plenty of critics), so as he's still trying to build his squad, he'll also find he's having to recruit replacements for those he signed and we've then sold. Don't know the answer to that, but it's something that's been dogging us for years.