I don't believe either question is addressed by the ASME code.
Do you mean maximum spacing or minimum? Are you trying to fit a bunch in, or very few?
One of the tank codes specifies minimum 4, one code specifies minimum 6, each with a maximum spacing of 10', if that helps.
On the minimum spacing or maximum size or number of bolts, it would depend on the details. If you're using individual chairs, typically space between chairs is double the chair width or so.
If you have a continuous ring or flange, I assume the minimum spacing would be dictated by socket or wrench access.
Also, coordinate this with foundation design, if you're coming up with more bolts than you can fit on it, you may have problems with concrete compression and embedment.
In that case, also consider higher-strength bolts if they are an option.
I suppose the base could be flared out more to ease some of the issues.