Personally I’d say if you’ve got that far in SSiW, and based on the questions you ask being similar to the things I wonder about myself, that Thinking Welsh would be right up your street. It’s excellent for dipping in and out of and as a general reference. I’ve not needed to ask as many questions in the forum since getting it, which is sad in a way.
My only criticism (sorry @garethrking, I’ve held this in for months by now) is the way the book has been typeset. The headers of the page are useless as they don’t change apart from the page number, and the page numbers aren’t used in the contents or index. It makes finding things quite frustrating as you can’t see the entry numbers as you flick through, and I regularly forget I am even looking for an entry number instead of a page number. I hope this gets fixed if there is ever a 2nd edition.