If you wanted to do both AL and NL, you could use something like the following settings: In addition to the usual positions, you could have an extra middle infielder, an extra corner infielder, one extra outfielder, and 1 or 2 extra util players. This would make the offensive depth roughly on par with a standard 12 team league. As for pitching, it seems as if you use weekly lineup changes. Use k/9 instead of k's and put a transaction limit of 30-40 for the year.
You basically have to decide if you want a super deep league (8 teams in NL only is like a 16 team league with both AL/NL) or if you would rather try to adjust your settings to mimic the depth of a standard 12 team league. I don't think you want an 8 team league with standard settings that has the full mlb player universe--there's just too many good players.