Answer: Unfortunately, I know of no alternative beyond natural rainfall, hand watering and mulch if you are not using an irrigation system. (The rain and mulch should also be accounted for when you do use a watering system.) The mulch is important in that it will break down over time to help feed the soil, help limit weed growth/competition for your new plants, and help maintain a cooler moister soil during the summer. The organic matter also helps to increase the air and water holding qualities of the soil, both of which are important for healthy root systems.
For a project of the magnitude you are describing, you might work in zones with some limited piping to deliver water to stations where you can at least fill buckets. Alternatively you could look into renting some sort of towable tanker wagon. If these options are not possible, you might phase the work so as to minimize the labor and risk each season.
Should you be fortunate to plant in a favorable year, your watering will be more limited. Should you have the misfortune of planting in a dry year, you could lose many of the new plants even with watering. I say this from sad experience.
Careful selection of plants suited to the native soil and natural moisture levels within the microclimates of the site combined with careful soil preparation and a layer of several inches of natural mulch can go a long way towards helping the plants take hold and succeed, but in a dry year there is almost no hope without water.
Most of the plants you listed do best with an evenly moist yet well drained soil, the possible exceptions being certain wildflowers. These plants tend to be particularly sensitive to dry soil. Eventually, once the plants are established, they should be able to survive without supplemental water -- but in a situation of extended drought even these plants that have been in the ground for three to five years minimum will suffer just as the naturally growing woodland suffers. It is a sort of survival of the fittest at that point.
With kousa dogwoods, please keep in mind that this tree is not a one for one substitute for the understory tree the native dogwood. The kousa dogwood requires more sun than shade in order to thrive and bloom nicely.
I would suggest that you spend some time testing your soil and researching the growing conditions you have to offer, then working from there, determine which plants are likely to do well for you. You may find some clues by looking at the plants already growing there. A naturalist, your county extension, and knowledgeable nursery staff can all help you in deciding what to try. Over time, and with some experimentation, you will discover which plants do best for you -- and which watering methods work well for you.
Good luck with your project!
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