Your method of sowing seeds will be determined largely by what you intend to do with the mature plants. If they are for the outdoor garden, enough will be needed to justify the use of large seed flats. If the plants are for the greenhouse, you will want a smaller quantity, and small fiber flats will be adequate.
You can sow seeds in one of the sterile mediums that you can buy, and this is an easy way to do it; or you can prepare a special soil mixture. However, you will get excellent results from sowings in milled sphagnum moss, vermiculite, or perlite. No harmful fungi are present in these and all are moisture retentive; seedlings are easily transplanted from them without disturbance to delicate root systems, for the material clings to make a little clump around each tiny network of roots. However, plant food must be provided soon after seedlings poke through, as these sterile mediums contain practically no plant nourishment.
Milled (pulverized and sifted) sphagnum moss is a superb seed-bed material. The danger of damp-off that dreaded fungous disease that causes infant plants to collapse and rot is minimized, for drainage is excellent and substantial root growth occurs.
Vermiculite is composed of expanded mica flakes that are very light in weight, yet retain moisture evenly and allow good air circulation for roots. Be sure to get the small-particled horticultural vermiculite; you don't want the coarse, treated type that is used for insulation because it may be toxic to plants, as some gardeners have learned to their sorrow.
Perlite is exploded lava, a white, glass-like silica derivative that weighs about one-tenth as much as sand. It has a slightly acid reaction but not enough to bother most plants. Sand mixed with peatmoss or sphagnum is good for seed sowing, also, but as with other sterile mediums, plant food is eventually required. Sand by itself won't do for sowing seeds, because it lets water run right through and does not retain the moisture that is needed.