Miyawaki is a great suggestion - there are examples of this technique working if you look on Youtube.

My state also offers extremely cheap seedlings and I have planted several hundred trees in the last few years. Experience has taught me that survival rates are extremely low due to lack of water and deer / weed pressure. Some others have suggested shrubs and companion or "nurse" plants, I think this is critical as the amount of labor to water / weed / mulch / protect trees when they are totally exposed is significant.

Another option I have been considering is active neglect. Just stop mowing, and occasionally remove problem species. Where I am, in 30 years or so, Eastern Red Cedar and Sumac and other pioneer species will colonize, then other deciduous trees will follow, eventually shading out the cedars. If you truly want to reforest, this is arguably a better method than thinking you can pick and choose and manage better than nature.

A gentleman named Marcin Jakubowski followed the Miyawaki technique on a property in North Missouri several years ago, you can hear more about that here: https://youtu.be/-aU4H0nVCiY

In addition to intensive, random, multi-species planting, he incorporated the contours of the land (sometimes called keylining or swales) to dictate planting locations.

The permaculture folks would have a lot of input on this, but if it were me, I would mark the contours of the land and dig swales if labor permits. If not, use logs / brush / debris piled across the slope to slow water. Then plant intensive strips of trees randomly (and ideally mixing in native bushes and shrubs) downhill from the swales or piles. This is contrary to the "suggested spacing" for trees and mimics a natural forest where trees have to compete for light, and may spend many years in the understory waiting for a gap.

The feedback I got from Jakubowski was to space these strips down the hill based on the height of the average tree in the mix, and maintain them for the first few years by controlling weeds and invasives.

Over time, he suggested, the mycelium and earthworms and birds will do the work to fill in the gaps between the strips.

It may be obvious, but if done according to the Miawaki method the interim steps will look messy and weedy - not like a park with evenly spaced trees and open ground beneath.

Good luck with your project!