Interest should be drummed up once the logo is decided on, then turned up a notch leading into each of the key stages listed above. I think once it's open source plenty of people will jump on board but if it's enough publicity beforehand, there will be a lot of people wanting to get in before it actually becomes open (hopefully not too many specualtors).
We must leave some margin for errors and hiccups. Anonymity is a huge task and it's unlikely everything will go without unforeseen problems. If you have attracted the spotlight while going live and you have problems after official launch / post-beta (a likely scenario), it can instantly turn around and people say "oh its broken" even if some things just need a bit of fine tuning. Bitcoin is 5 y.old code and is still patched quite a lot (0.90 changelog quite extensive), so, naturally, a few months old code that is not reviewed will require patching, hardening, etc.
Now this margin can be achieved in two ways: Not attracting too much attention OR attracting attention with a footnote that it's still in active development or something.
Of course margin for error is a good idea. I think with a footnote is the best option so each key moment can be used as a marketing opportunity. It probably is a good idea not to make too big a deal of it at each and every stage listed above - people may begin to think it will never be open sourced - but enough to keep it on people's radar and hopefully attract some early investors who know a good thing when they see it. As long as people know it's a work in progress they shouldn't get scared off at slight hiccups.