Hey,
Personally, if this were me, I'd focus on making sure that traffic loss was kept to an absolute minimum when I launched. To do this, I would take a crawl of your current (live) website and get a list of all URLs and do exactly the same for your new site (dev site).
You'll want to make sure that you map out 301 permanent redirections for all of the URLs from your old website and point them to the most relevant URL on the new site. For example:
http://www.yoursite.com > Add a 301 permanent redirection that goes to > https://www.yournewsite.com
That way, you will maintain as much link equity as you can and look to maintain your traffic levels when you go live.
As well as that, make sure you complete the basics;
- Meta optimization
- Fix any broken links
- Complete an audit to check for improvements
- Image optimization
Those are just a few, but there are loads more than you can do. Check out this post from the Moz blog for some extra help.
Hope this helps?