We expect authors to email the pdf file of their paper by July 14, 2019.
There is no page limit, but please be conscious that the longer the paper, the less chances that reviewers accept to look at it.
A paper submitted to the special issue which only contains the proofs missing in the conference version is not what can be called "substantially extended version".
We recommend you to use the Elsevier article class elsarticle.cls (http://www.ctan.org/tex-archive/macros/latex/contrib/elsarticle) to prepare your manuscript and BibTeX to generate your bibliography. For further information, please have a look at the instructions at the Elsevier page (https://www.elsevier.com/authors/author-schemas/latex-instructions).