2. If you want to run a sizeable launch, then JVNP is the site for you. You should see if you can get a premium mailing from Mike. These mailings will get you a lot of exposure, lots of JV partners, and lots of street cred.
If you just want to attract JV partners here and there to maybe make some money here and there, you could try the Warrior Forum's JV section. WF and JVNP are the only two IM-related sites I visit regularly, so I can't recommend any others.
1. For your first ever launch, I would get one JV partner as soon as your product is completed (or, if it's a software you're selling, when the beta version is done). Use that JV partner to test conversions on and make tweaks as necessary. Then, once you've got some nice numbers to show to Mike (or some other JV broker), go for that premium mailing. This route is much better than setting up shop on the side of the cyberstreet and frantically waving your arms for attention from potential JVs.
For future launches, you'd already have a list of your old JV partners, so you would not need to look far for people to promote your future products.
Make sure your launch date is flexible - stuff happens. Also make sure to give yourself plenty of time between now and your planned launch period to coordinate with your team if you have one, to do pre-launch if you want one, to perfect your product, to test your conversions, to give your JV partners enough time to slot you in, and all that good stuff.
Good luck! Hope I haven't vomited too much for you to digest here
Curtis
P.S. I'm not an expert...I am actually looking forward to when the real experts show up with more thoughtful answers :P