Shall i go into flower?

It will be best to correct the phosphorus deficiency before flipping os your plat will get worse if flower

how much space do you want to fill? Expect it to double in size... nearly double in height is a safe guesstimate for most. But with double area you must consider it's a lxw product, so .75x.75 is about 1/2 of a 1x1. so, a bit less than 3/4 your L and W dimension should be safe when it comes to area... height is easily measured unlike the area. This is 100% about the space you want to fill or maybe a time constraint. So, 100% upto you what works best for your context.