Viruses are rarely seen and I've yet to see leaf-nematodes cause trouble. I have found that mildew can be brought on by drought stress which is another reason to use a moisture retentive but well draining compost. We don't have snails in Oregon to any degree, but I have been told that in the UK they are a big problem with lungworts. Propagation of Pulmonaria is quite easy. Divisions can be made in late spring and root cuttings can be made over the winter months.
Seed is variable in outcome, but is very large and easy to germinate.
The most difficult part is in the collection of fresh seed. Looking into the calyx after the flower has dropped off, you will see the single seed developing. Over the next few weeks the seed will change from white to black and will detach with the slightest breeze and disappear unless you construct a collection facility of some sort. Most gardeners let nature take its course and find many delightful seedlings about the garden. Bumble bees and honeybees are rabid pollinators which I have watched flitting from one specie to the other.