Domain & resolution

First you should decide if your final(!) simulation (see "Cascading" below) should be on a regional or a global grid and at which resolution you want to run. For this it is important to know that:

Number of points

Resolution → timestep

Resolution → timestep → radiation timestep

Resolution → (non) hydrostatic

Cascadeing

Spectral nudging

Period

Initial conditions

Driving data

Geophysical fields

Schemes

Land surface scheme (ISBA, CLASS, SVS)

Lake scheme (non, FLake, CSLM)

Urbain scheme (non, TEB)

Microphysics

Precipitation (Bourgouin)

Boundary layer

Horizontal diffusion

Output fields

Output fields

Instantaneous / averages / min / max

Initial condition fields

Pilot fields (2-D / 3-D)

Output frequency

Output levels

Size of output files (monthly/daily/hourly/...)