Being realistic here.

12x new buses for the X15/X18, 7510 - 7512 and 7514 - 7517 35 and spares, 3 Omnicities withdrawn, 1402 withdrawn, 7529 - 7533, 7553 - 7556 for X14/X20 - increase X21/X22/35 back to every 20 minutes each (prefer coaches but will be Enviro 400MMC's)
Ex London Gemini's to replace all the Pulsars on the 306, X7/X8/X9
Ex London Gemini's to replace the B7TL's on the X46 into spare role and few extra to withdraw the Gemini B7TL's.
18x replaced Pulsars at Blyth / Jesmond replace all the Omnicity's which are withdrawn (3 replaced by Enviros at Ashington). Keep other 5 at Blyth possibly for the 1/2.
New minis to start to make progress on the Solo's (Enviro 200MMC's)

Should be enough to get through to 2024/2025 when investment really needs to be done.