We planted an acre of wood about 4 years ago, with help of woodland trust. They advised us to plant randomly in groups of about 7 trees of each species....(single trees wood be smothered by stronger spicies.)
In practice we started with the species we had fewest of and planted the groups at opposite ends of the field. Then went to the next spices, picked up 7 ish plants wandered of and planted them and so on.
I seem to remember spacing was approx 2.5 m....but you can work this out by dividing the number of trees you have by the area you are planting.
Our trees were wrapped in sets of 25, so that gave you 3 groups, an 8 an 8 and a 7 worked quite nicely.
It's not rocket science, most of our wood was planted on Xmas eve ! We followed on with stakes and tree guards over the next few days after Xmas day of course. Whether you risk leaving them unprotected for a few days depends on what wildlife you have around, you may want to guard as you go along.
It's a very rewarding experience, and we love walking through our wood in the evening doing a bit of maintenance.
Oh yes we bought some wild flower seed and sew the area too, it was expensive but lovely to see the colours now a few years later.
How much are you planting out of interest ?
My wife has just reminded me we put the stakes in as we went along so you could see the area we had planted, as we soon realised you couldn't see where the plants were otherwise !
Ours was a grass field which we ploughed and rotovated first.