Elder is great for wildlife but it grows much quicker than the others and soon pushes them all over and shades them out. We have just been eradicating some of the elders we planted in a bit of woodland 10 years ago, and thinning the rest drastically. So leave a lot more space for elder than for slower growing trees, or be prepared to demolish them.
We have what sounds like a similar strip of woodland stretching along the roadside, which we planted up with trees about 15 years ago, then filled in some gaps maybe 5 years ago. As well as elder, holly, hawthorn, and hazel, we included a couple of ash, and there was one there originally, plus a couple of oaks donated by friends who had grown them in pots, silver birch, rowan, mirabelle, willow, roses and then a few scots pine and juniper, and one balm of gilead for the sweet smell in spring. I think that's it. Oh no, there's also a conker tree my sons grew in a pot decades ago
The hollies we tend to plant in groupings of 3 or 5, rather than evenly distributed, so there's one male to a handful of females for berries.
One rose has been allowed to grow into a large impenetrable thicket, which is gorgeous when in flower, and shelters lots of creatures. Other roses have a more vertical habit.
The mirabelles are fast growing for keeping out prying eyes, and in spring are covered in may-type blossom, then lots of red or yellow small fruit for the birds, or us.
The whole planting is higgledy-piggledy, not in rows, with the odd tree fitted in here or there when we have them, so different ages too. The slowest growing are the junipers but we put them in as they are a local native which has been almost grazed away in the open countryside.
Our trees in that bit are now big enough for bird boxes, which we put up earlier this year, and wild birds have been nesting in some of the larger trees already. The willows are large enough to have been cropped (coppiced or pollarded). The hazel have had nuts on for the last couple of years - we grow those in small groupings too.
We have underplanted in patches with snowdrops and primroses, and may add bluebells this autumn.
For judging planting distance, visualise how big the tree will grow, and the one next to it, then leave an appropriate distance between them. For trees like birch, they are not a long lived tree, plus they are light and airy, so plan on removing them in 15 to 20 years, with slower growing varieties to then have space to grow on. Taller trees will eventually grow higher than others, so you will have several layers of growth, which looks very natural.