Hoping someone can help.
I'm wanting to purchase some plug plants of:
Is it too late or the wrong time of year to do this now, if so what time of year would be the best time to do this?
I would definitely wait till spring. Perennials are dying back now and they will be too small to plant outside, so you would have to nurse them through the winter somewhere under cover and watch out for the first signs of growth to protect them against slugs and snails. In spring they will get away faster and grow more strongly, so they will soon be large enough for you to plant out and you will be able to see them to keep an eye out for molluscs etc. You might even get flowers on your betony and fleabane. The others are spring flowering so probably won't make it till the year after.