Should I use weed killer before turfing ?
west central Scotland
All those plants mentioned are hardy and easy, and will only require minimal maintenance once established. You can add spring bulbs into the mix as they will be fine, assuming there's enough light there - it looks like the big tree has high enough canopy even if it's evergreen. You would plant them along with the other plants wherever possible, but it's easy enough to push some in at a later date.
Spacing depends on the eventual size of each plant, so it's a case of doing a little research. The general conditions you have will dictate though - some will grow slightly less, and some may grow slightly more.
Another common, but excellent ground cover plant is Cotoneaster. On a slope, it knits the ground together too, although that isn't particularly steep.
It's a place where beautiful isn't enough of a word....
edited August 2020
The plants mentioned are hardy, spacing depends on the plant - things like Ajuga would be on about 33cm centres for it to knit together relatively quickly. If you just want extremely tough no-nonsense ground cover, rather than anything fancy, I would go for Prunus 'Otto Luyken' or Cotoneaster dammeri at around 45cm centres (or both, bearing in mind the Prunus will grow to around 4 ft tall and can be sheared to keep it low, whereas the Cotoneaster is only a few cm tall and hugs the ground).
You can plant them further apart btw but it will take longer for them to knit together and form a continuous ground cover. 4-5 plants per sq. m is what car park landscaping is based on!