GardenersCardiff answers:

In Zone 5, I usually plant the garden in mid-to-late May, depending on temperatures and forecasts.
I only grow tomatoes and peppers from seeds started indoors. I grow beans, cucumbers, zucchini, lettuce, spinach from seed planted directly in the garden when it’s warm enough, and I usually grow a few nursery-bought transplant seedlings.

I’ve found that it’s best to start peppers very early; about 10 weeks before the intended planting date. I start tomato seeds about 8 weeks before planting in the garden.

My recommendations for indoor seed starting:
I prefer yogurt or margarine cups with seed-starting soil mix to jiffy pots or tiny cell trays. (I want the plants to be quite large when they are planted in the garden; don’t want to bother with repotting them into larger containers while they’re growing indoors).
I poke or drill holes in the bottoms of the containers and place them on trays so the plants can be “bottom-watered” (pour water into the tray and allow the soil to wick-up moisture, rather than watering the soil surface which can disturb seeds or tiny roots and often contributes to mold/fungus/disease problems).
I cover each container with a clear sandwich bag to maintain humidity and remove the bag promptly when each seed sprouts.
A seedling heat mat helps to speed-along the germination process.
If you don’t have a sunny window in which to place the containers, use artificial light. No need to invest in an indoor greenhouse or a complete grow light apparatus; a flourescent fixture with a full-spectrum bulb or one “warm white” and one “cool white” bulb works fine. It’s important to position the light very close to the tops of the plants. Hang the light fixture with eye hooks and a chain on the underside of your kitchen cabinets, or use scrap lumber or metal to fabricate a stand from which to hang the light. It should be made so that the height of the light can be adjusted as the plants get taller. (I subject the seedlings to 14-16 hours of light daily)
A small fan blowing gently on the seedlings for a few hours daily will strenghthen the stems and help to reduce the common mold problems on the soil surface.
Plant about three-times as many seeds as the number of plants you would like to have in the garden. As the plants sprout, you can remove the smallest or weakest-looking ones in order to hopefully have the best quality plants to place in the garden.
About a week before planting outdoors, introduce the seedlings to the weather by first setting them out in a shaded area for a couple of hours, and gradually giving them progressively longer periods of full-sun exposure (make sure to monitor the soil moisture at this time).
When it’s time to plant in the garden, remove all leaves except for 4-6 at the very top of each plant. Plant them DEEP in order to encourage a large, strong root system (ex: only 2-3 inches of a 6-8 inch tall seedling may be visible above the soil surface when planted; don’t worry, they’ll grow quickly this way).
Good luck!