Hi, Tammy ... much success with your first launch.
As this is your 'maiden voyage', I'd spend as much time as possible connecting with your contacts and doing what you can to get a launch support commitment from them, perhaps even ask a few of them to help out with test traffic so you can tweak the offer, while introducing yourself one at a time to other proven potential JV partners, well in advance of your launch.
Unless you have a significant self brand in your industry, going into the affiliate recruitment phase of launch preparation with no previous product launch track record and without ample time to develop rapport with new JV prospects, is a recipe for disaster. Do please take the time to make sure your conversion and retention is there before inviting those outside your circle in, and have enough core support to get the ball rolling on launch day without relying on the unknown (AKA random affiliates you have no rapport with).
Once you have at least a small number of core JV partners confirmed, start qualifying the rest of the JV leads and do your best to stay in touch with those that have shown promise. 10 proven JV partners that you know will promote for you is worth 100+ random JV/affiliate leads that you have no history with.
On launch day, I'd send out a JV notification just prior to launch to get the ball rolling, then send one every 24 hours at approximately the same time of day, with positive numbers (units & sales totals, conversion %, EPCs, etc), social proof (partner/customer testimonials, named sales leaders, spotlight on strong performing partners, etc.), launch phase details (ad copy, links, etc), affiliate area log in details (if necessary) and a teaser mention of what's to come in the next mailing.
As far as the length of the launch, will there be a pre-launch phase?
If you decide to go the 7 day route, make sure that you have a strong launch phase planned for Friday to spike and carry the interest and motivation through the weekend and have something big planned for Monday to close things out (assuming you're running Monday to Monday or Tuesday to Tuesday). Otherwise, you might start losing affiliates to the new launches starting on Monday/Tuesday before you get the last spike in.
Or you could go with a Monday to Friday 5 day ... both work. Your strategy, JV/Affiliate management and other factors and variables like competition, timing, etc. will decide how well.
Hope that helps ..
Looking forward to seeing the additional responses.