The original text of Second Stage Lensmen was significantly modified for book publication, so it now gives away things which were not given away in the originals until Children of the Lens.

I could see either reading the core four books first followed by the frame in Triplanetary and all of First Lensmen; or on current series order. FWIW, I began with FL and SSL, which I took out of the library together, and it din not impair my enjoyment.