The coil required for a particular application will depend largely on the method used to drive the coil and the spark energy requirements. Consult the igniter manufacturer for a recommended coil for use with a particular igniter.
The required Dwell Time will be entirely dependent on the coils inductance. Dwell time should be correctly set to avoid damage to coils and igniters and also ensure adequate spark energy. It is not true that increased dwell time will always result in increased spark energy.
Use only coils designed for high-energy transistor/inductive ignition systems. The coils primary resistance should typically be between 0.4 Ω and 1.0 Ω. This applies to both single and dual post coils in distributed and multi coil applications.