Re: maximum resolution (# of voxels) of OpenLB
1/ Actually, there is no limit but for the used hardware. The bigger the used maschine the bigger the simulation you can run. We do simulate about 1 billon cells on about 1000 cores.
2/ I would run a convergence study to answer the question. Chosing one fixed geometry and solve it by varying the resolution. Then, you will know what resultion gives you what error.