Here is my suggestion:

7x Plaxton panther LEs (with rear axel steering) for the X20 (+2) spare
Features: high backed seats with seat belts, free WiFi, USB charging & wheelchair ramp & bay

6x Plaxton leopards (like the Lothian Country ones) for the X14 (+2 spare)
Features: high backed seats with seat belts, Free WiFi, USB charging, curtains, quiet low emission engine & wheelchair ramp and bay

7x Plaxton panoramas (with rear axel steering) for the X15 (+ 2 spare)
Fearures: high backed seats with seat belts, Free WiFi, Toilets (if facilities in the depot allow), tabels (4 on each deck), USB charging, wireless charging, seat back tray tabels, curtains, quiet low emission engine, wheelchair ramp and bay

Cascades:
7401-6 to Ashington for the X18 (temporarily to mermanent dependent on a sustainable bus/coach being found)
7511/2 kept as spare decker at Ashington replacing 7484/6, 7514-7 to the Belmont for th£ X12 releasing 4 pulsars to blyth replacing 1401-3 with one extra spare, 7529-33 to Redcar/Whitby for the X93 (+2 spare meaning only 1 spare ALX needs allocated in the summer) finally omnis cascaded around the region or country.