Maybe Warrington, as you could develop the map in stages, Starting with one side and then developing the other when ready?
Notable routes in W'tn East: 17(17, 17A, 17C), 20/21 (The Pops), 25 (26 & 27 On Sunday)
Note: Since the 19 & 28 leave warrington, these could be AI routes to begin with?
Notable routes in W'tn South: 1,11,2,12,10A, Cheshire Cat
Note: 'Cat' Buses leave warrington, these could again be AI to start out
Notable routes in W'tn West: 17,32 (Blueline) ,18 (Runs once a day to Priestley college), 16(A)
Note: 32 leaves Warrington