While growing tomatoes in Eastern Mass, a tricky variable spring climate, I hardened off for 7-10 days. I have been known to cover over the tops of flats with plastic wrap with several vent holes but that might be overkill. If you do that step, you need to open the 'tent' during the peak of the sun to dry out the soil. This can be way more fussy than most would want. This step does give more yield though.
I'm careful to water (w/ sprayer) JUST enough to keep to keep the soil moist but not invite mold or fungus. I'd put the flats outside for a few hours (avoiding scorching sun), then for half a day and finally for whole days at a time, while avoiding brisk winds. After 10 days, the strongest survivors make it to planting bed. Any seedlings that don't grow tall I toss or add to my compost.
Yes, snipping off the bottom leaves in an established plant will help the plant focus it's energy. However, in a seedling I'd be careful not to stress out/bend the thin stem. I've croaked a few while trying to do that.
Finally, I plant those seedling far deeper than I used to do...perhaps in a mound that covers the point where the first (snipped leaves) would have been. Some folks plant in a mound sideways up to half of the length of the stem, giving the plant lots or room to grow new roots..
Oh yes, I always toss in a little bone meal and very mild fertilizer, with a little good soil from a mature compost pile that hasn't any newly decaying matter still in it.