Thinking advice pls

Auk mini, about 3 weeks in and growing nicely. Need some advice on how to thin the parsley, coriander and basil seedlings. They're in position 2,3,4, sown to the density suggested, and I'm thinning as they come through. Just need to know at what point should you stop thinning and how many plants you let grow through to harvest?

Second question, looks to be a little mould developing on the salad leaves in position 1, on the top of the soil, what's the best approach to keep that away? Thanks all and happy gardening!!