ABC...

Annie, Boco, Clarabel, Duck, Edward, Fireman, Gordon, Harold,...............INK!!!
And it was all going so well.

[Super]

I can't make out the writing, is there any other non-character letters?

Looks like:
Annie, Boco, Clarabel, Duck, Edward, Fireman, Gordon, Harold, Ink, James, Mrs Kindley's Key, Luggage, Mill, Notice, Oil, Percy, Quarry, Ruins, Sir Topham Hatt, Thomas the Tank Engine, Umbrella, Viaduct, Whistle, Xylophone, Yard, Zigzag.

Oh, yes, the Fat Controller's a maestro on the xylophone, there's not many people know that.

[Super]

Oh, so they aren't all characters names. Maybe thats what they should do...introduce new characters to fill out the alphabet. I = Isabel.

I know this was probably made before season 4 came out but Rusty>ruins

Oh, so they aren't all characters names. Maybe thats what they should do...introduce new characters to fill out the alphabet. I = Isabel.

Don't need to make up an 'I', Railway Series No.40 - 'New Little Engine'

[Super]

There ya go, the 'I' is covered.