From my understanding when using hreflang to denote English speakers in the entirety of the European Union you wouldn't need a regional tag on there.

I.E. if you targeting English speakers in Canada it would be "en-ca" whereas targeting English speakers in the UK would be "en-gb". But when targeting English speakers in all 27 (?) EU nations at once then you would just use "en".

True true. SERPs for a singular will not be 100% the same as SERPs for the plural in many cases but there are often overlaps. Keyword research will help in determination of which may be the better trafficked and/or more valuable term. Natural inclusion in the body can potentially make up for lack of inclusion in the title. Also, considering that Google will in some cases change your title and description to better suit a searcher's query for which you are also relevant, you can't rely too heavily on title optimization alone as a factor in your ranking though it is a viable signal.

In most cases Google is smart enough to understand that a page relevant for "Wood Desk" could or should show up in searches for "Wood Desks" and vice versa. As such, it's not really necessary to make sure that you shoehorn in all of the plurals and singulars of your core terms. Worry about it more from a Human standpoint. Making the title more human accessible will help with clickthroughs, visits, and so on. Forcing multiple variations of the same word into a title in order to attempt catching every variable will probably make people skip over you. And ultimately, getting the qualified traffic is what much of SEO is about.

Spammy domains have been known to overuse the Hyphen... but using Hyphens does not make you spammy

Matt Cutts had previously stated that Google recognizes the Hyphen as a separator and the Underscore as a connector... i.e. "red-wigdets" gets read as "red widgets" while "red_widgets" gets read as "redwidgets". For keyword purposes, a hyphen is technically better but the difference is likely negligible. Also keep in mind the EMD update. If your core term is "cheap red widgets" and your domain URL features "cheap-red-widgets" then the EMD has made the previous positive name correlation into a less powerful signal.

Matt Cutts 2011 Underscore vs Dashes in URLs video http://youtu.be/AQcSFsQyct8

Matt Cutts 2009 Underscores or Hyphens in URLs video http://youtu.be/Q3SFVfDIS5k

Matt Cutts 2005 Dashes vs. Underscores blog post http://www.mattcutts.com/blog/dashes-vs-underscores/