Sorry -
SEO (Search Engine Optimisation) .... the URL/Domain can assist in what is loosely termed as 'ranking' if there is match between URL/Domain, Keywords, Description, Titles etc.
I am not sure whether separation by a hyphen (which definitely works) is more, less or same effect as a numeral such as 4.
4 would suit me for branding purposes, but do not want to screw up
SEO in the process.