For GNFS jobs, I start sieving at 1/3rd of the factor base bound. The original factmsieve script started at 1/2 the bound, so somewhere in that range is reasonable.
If your tools don't supply a default factor base (factmsieve.py does) it doesn't matter very much (within a factor of two of "best", say) what factor-base bounds you pick; perhaps 30M for the bounds with sieving starting at 12M should work fine. 14e is probly best; if you want to play with a little test-sieving, try using 14e the regular way and also invoking with with "-J 12" in the flag list. The latter may be a bit faster, at the expense of less yield (and thus a larger range of Q to be sieved).
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