It doesn't seem like this forum gets much attention so I will offer a little of my limited knowledge.

Your lights will be fine to start seedlings. Just don't start them too early or they could get leggy and weak.

I would research each species to find out what works best for germination.

I agree. Your light set-up should be fine for growing annuals/tender vegetables. You should start them indoors 8-12 weeks before your last frost.

agree. I have a set up at home using shop lights hanging on chains. Make sure your lights are just about a foot higher than the plants. This ensures your plants don't get too leggy. As they grow, adjust the distance of lights.

I have 2 48" lights with wide side reflectors and T8 daylight bulbs and let me tell you stuff grows like crazy under them. Anything I've put under them has done well so you will have no problem. Make sure when they are mounted you have enough room to raise the lights as the plants grow. I keep the tops of my plants an inch or less from the lights but not touching the bulbs. The further away the lights are from the plants the less concentrated light the get.

I have mine plugged into a power bar and then into a timer in the plug in on the wall. The timer is set to come on at 6 am and go off at 9pm. That gives them 15 hours of light

I've been toying with the idea of adding more but space is an issue and I do have my greenhouse