Hey brother, I wouldnt worry at all about the electric when your only adding 125 more watts. What is your fan type and size? I have a 400 watt MH and a 4" inline centrifuge fan for exaust. The fan pulls 80 watts. I also have 2 small Air King 2 speed fans for extra movement. They pull about 20 watts each. You could put more than 5 under it brother, dont listen to the haters. I worried about my electric bill at first but now I'm gonna add supplemental light for under the canopy when its time to.
Look up LST Training your plants, its a great way to keep them tighter or shorter or however you need to use your space. Really though, it all depends on your set up and air exchange, nutrients, watering schedule and other environmental factors like humidity and average temp. When they say its all the little things that make a difference, it really is true. All those little things make your bud yield way bigger and way higher quality too.
If you go and look at my pics of my set up you will see that I currently have 20 total under my 400 watts. 18 are Lemon Haze seedlings that are not sexed yet and 2 are larger females of a purple strain that is unknown to me (The 2 seeds came from a bag of some of the frostiest purple bud I have ever seen and my buddy was saying that "This stuff rarely comes around and is called THE PURPLE FROST"). I never told him of the 2 seeds (both were girls obviously and wanted to explode into flower when I flipped for sexing) and I cant wait to give him a nug of that same herb and him look at me like, How did you meet him/her?.
I'm am hoping to get at least 9 females out of the 18 so I plan on finishing 11 total under the 400 watts. I will be adding supplemental lighting for the under canopy also when it is ready for it (pretty soon). Do look at the LST Training if you need to fit a lot more in a tight space or if you want a big yield with limited space. I'm going hydro next grow. Way bigger results for our size grows. At least a 3rd better yield, maybe even double with hydro over dirt.
God bless brother, Happy growings. Peace, J
p.s. RG3 is the man, what a game huh? Pierre-Paul couldnt judge his hip movement for direction on where to meet him with the hard hit. This is rare in a QB and with his other natural ability, I would say he's gonna be breaking records in about 10 years if not sooner. Peace, J