Advice Needed on 2nd grow. How much light for 2 moms?

So my first harvest is a few weeks from being finished. Things are looking good but I need some advice on what to do next. I have about 30 seeds from some bagseed I had awhile back which I really want to get started. But the thing is I really don't want to lose the strains. I have 15 seeds of 1 strain and 15 seeds of another. I want to start these seeds, pick out the best mom for each and keep them as a mother. My question is, how much light am I going to need to keep 2 moms going? I have a 600W HPS which I am using for flowering. I was also just given a 1000W MH. I do not use this light because the breakers will not allow it. My grow room is in one of the spare bedrooms in the house. I need to get the breakers fixed. How much light would I need to keep 2 moms going and take clones every month or so? I have a 4x4x5 box that my 600W HPS in in. I want to have these 2 moms that I will take clones from every month or so and put these clones into the flower room with my 600W HPS.

So how much light would I need to accomplish this?

Or would the best option be to get my 1000W MH going by fixing the breakers? If I had the 1000W MH to keep my moms going and veg the clones I know it would work. But I think this is a big overkill on how much light I actually need. I grow for personal use and I feel like a 1000W MH is a big overkill on using it as a veg light considering my flowering light is a 600W HPS...

This is why I need advice on what to do! Any help is appreciated.

Roughly 20Watt/Sq. Ft. will be fine for Moms.

Alright thank you for the reply I will do some more research..

i now have the option of using a 150W HPS as a veg light. I know MH is better for the veg stage but would a 150W HPS work fine? Would it be worth it to invest in a small 250W or 400W MH light to veg or would a 150W HPS be fine?

Any advice is appreciated.