dude, i share ur pain. when i first looked at mh, advises were coming in thick and fast, and they are not necessary the same.
since ur going for lps only, u can stay with 150W but go for 2 units for even distribution and can hang 9" fr water level. but if going for one unit, need to put very near water.
i personally suggest u go for one 250W as what i have (although now im regretting it cos i want sps and thus need 1x400W or 2x250W).
if u like slighly blue colour, ie not normal daylight yellow or white, take 20K Kelvin bulb. im using BLV and the blue is sufficient such that u dont need to use actinic blue lights.
so in summary, make sure you are sticking to lps and not eyeing sps cos upgrading is always gonna cost more $$$.
cheers!