If you only have one 125watt i would only do 2 plants

and 4 sativas would be way to much because they get really tall, so there would be 4 tall plants branched out everywhere under one 125 wtt is not going to happen, it would just end up decreasin your yield and overall bud potency. More plants dont mean more yeild in certain situations...you can have 1 plant veg it a little longer, do LST or scrog to make it nice and bushy and it can yield as much as 4 overcrowded plants not getting enough light.

go with indica;s, or hybrids that you know wont stretch alot.. you could still grow sativas but under the floursecent it would be good to do a Scrog with 2 plants and a short veg so you can match up the footprint of the light to the screen and have the light adjusted the way you want it over an even canapony.

and some sativas take almost twice as long as indicas to flower...sativas take like 70-90 (some over 100) and indicas can be as short as 45-65

what type of system are you growing..hydro, soil? it can be more helpful as far as plant numbers go