Suggested tools within the editor to generate geometry?
Procedural Mesh. For example: you can use a function 'Get Section from Static Mesh' to create procedural mesh from static mesh which is contained in the engine. Or you can 'Create Mesh Section' from the arrays of vertices coordinates etc
Starter content i guess is also out?
Yep ) But you can use the templates, can create yours own materials (using the engine textures if necessary) etc.