No, those 2ft agroson bulbs will be perfect. And you can leave them up during flowering as well, it will more closely mimic the color signature of the sun than just a HPS bulb alone. If you don't ad some supplemental light in the blue spectrum, your plants will still grow and be healthy, but they will just grow at a slower rate. It will be best to wait until your plants are about a foot tall before triggering them into flower if you want a decent yield. When they go into flowering, the growth rate will increase because the HPS is the correct color spectrum for flowering.
As far as watering, there are two things that I go by. The first is that I put my finger about 2-3 inches deep in the soil. If it feels dry its time for a drink. The other is I lift the pots to feel the weight. If you pick them up just after watering, they will obviously be much heavier than when they are dry. After a couple of week you'll get a good feel for this. Some people wait until the the plant wilts, but I don't recommend waiting that long as it puts unnecessary stress on the plants. But on the other side be sure not to over water as this will cause the roots to rot.
I only feed the plants once a week, more than that is really not needed. Too much ferts can burn your plant and give your weed a bad taste if not flushed out towards the end of flowering.t. I grow in 3 gallon pots, so I'll run 5 gallons of plain water through each pot a couple times a week for a last 2 weeks. This flushes out all of the accumulated nutrient salts in the soil and sends fresh water through your plants flushing out all the toxins that give weed that harsh flavor, and this also makes your weed burn better as well.
As far as the leaves, once you get things in order, you'll have new growth. The damaged leaves may not recover, but that is not an issue.
Feel free to ask as many questions as you need to. That's what this forum is for. For us to teach you and for you to pass it on to someone else.