Hi Diana - no question is ever 'dumb' I bet even some of the more seasoned guys often learn something new
IMO SEO should be involved from the project design and architecture right through to content and of course launch and the life after the launch
Well, this is how I practice SEO in any case. I am of the opinion that SEO and web analytics go hand-in-hand as they are soooo closely related.
If the design is outsourced, and the designer knows SEO best practice so much the better. Both design and SEO are time consuming practices and, I am sure that the designer would not want the responsibility of the SEO on top of the design work - they wont have a life outside of work
SEO is not a once-off implementation and, if the site design is SEO friendly it is a great base from which to start a full round optimization strategy. SEO is an ongoing practice, as each day new competitors enter the index.
There will more than likely constantly be things that you 'tweak' on your site. Feg: if you regularly check the log-files then you begin to see a pattern in the user behaviour of your site. You will 'tweak' your site to fall in line with the patttern that you come across to benefit from the most conversions., etc etc
That is why IMO the client would still continue their services with you as you will focus all your attention to SEO.
Focus = results.