Launching redesigned website...best way... will redirect be needed?

I'm creating a website redesign for a client. The original site (48 pages) is built on basic HTML and though it's 10 years old and only has a dozen backlinks it does rank very well in local area Google serp listings for the root domain, unclaimed Google places, & various local directories that are listed within the serps (<--- mainly because it's in a small village & the domain name contains the niche root KW) The site gets no traffic to speak of... but it's 48 pages are indexed.

The new site is built on wordpress and is very thin (which is what he wants) compared to the old site... it really only has the home page & 12 photo gallerys (plus the normal about us, contact us, directions, privacy policy pages).

Once the new site is launched I do plan on doing some basic off-page seo like claiming his site in Google places and other various directories, as well as building some other backlinks.

Considering his current site really doesn't rank in the top 100 pages for any KWs (other than his domain name) and receives very little traffic... what would be the best way to launch his new thin wp website?...

Need I worry about doing re-directs for each of his old site's 48 INDEXED PAGES, or can I just take the site completely down & launch the new site?

Or should I approach this matter in a completely different way entirely?

Thanks,
CO