Hi Owen, there is some really useful info on this thread and David is great at helping us and being patient!
Sweet peas are fine with frost, David has told us this many times so I can answer that question.......they don't like being 'coddled' as David frequently tells myself and other mums on here who like to protect and nurture (he thinks it's a woman thing!! )
As for the leaves thing, I pinched mine out a couple of weeks ago as they had gone very leggy and they have been outside since, they are just starting it get leaf buds at the bottom now, I posted a picture further up last night and on the plant in the corner you can just seen them. I think I pinched mine out lower down though, after the second set of leaves maybe?
So I wouldn't worry, but no doubt David will be around later to tell you more as he is the expert