How can I get them strong enough to put them outside? Thanks!
If they are getting long and floppy, they are not getting enough light. Either put them in a brighter window of move them closer to the light. Placing an oscillating fan on them will also help to strengthen them.
When you are ready to move them out, make sure to harden them off. This article will help you with hardening them off:
I just turned on the lights on my veggie and flower seeds! Do I leave the diffuser on the bulbs of the fluorescent lights I installed, or do I leave them off?
I would leave the diffuser off. You will get a slightly more intense light with it off, which the seedlings will like.
I have taken off the cover over my seedlings and have also put a fan on them for air circulation, but the white fluffy stuff is still on the dirt. Is there anything I can put on the dirt that will get rid of this without harming my seedlings?
I'm assuming that you have tried the suggestions from the following article: https://www.gardeningknowhow.com/garden-how-to/seeds/preventing-white-fluffy-fungus-on-seed-starting-soil.htm
Evidently, the soil is still too moist; otherwise, the fungus would not grow. Are you watering too often? If so, allow the plants to dry out some. Let it air out for about a week, monitoring it often with your finger for dampness. If this doesn't help, there could be a problem with your potting soil--too heavy--or the container itself--poor drainage (check drainage holes). If the soil remains damp, you may want to consider transplanting (if feasible) using a lighter potting soil. Also, move the seedlings to an area offering additional light. When you do water again, try watering from the bottom rather than the top.
This is my first time starting vegetable seed growing indoors, since last year starting outside did not work. I started the vegetable seeds indoors in small flats, and in four days, the seedlings were going. I thought fantastic; it works. Another day later they sprang up with long, thin stems. Is this bad or good? Do I need to start over? Should I let them be? Should I try to separate them and put them in deeper containers?
If they are becoming "leggy", this indicates that they are not getting enough light. Move them to a location where they will get more light or move them closer to your light source.
I have been growing my plants inside for five weeks and they're ready to plant, I think. The daytime temp is around 70 but nightime is 35-49, with rain showers expected over the next three days.
Here is an article that you may find helpful: https://www.gardeningknowhow.com/edible/vegetables/vgen/when-to-plant-your-vegetable-garden.htm
Due to the recent hot weather, although all the doors and windows were open and a fan going 24 hours a day, all my bedding plants have bolted. Is there anything to be done so they can be used?
No, once they start to bolt, you cannot stop it or reverse it. You will have to restart them.
When I start my plants from seeds, they grow long and slender instead of strong and firm. What could be the problem? I start them in the kitchen using starter mix in peat pots.
Young plants grown indoors need a fan blowing on them to imitate the wind outdoors. This helps to grow thicker, stronger stems. Also, if they don't get plenty of sunlight, they will grow tall and slender. One more thing, at night the plants should be placed in a cooler place to help grow healthy stems.