Just curious how many users should we plan for when launching. Also, is it too early to move to dedicated server or stick with virtual share hosting?
If you're in Europe, take a www.Hetzner.de/en dedicated server, 49 EUR/month is a small fee to pay to avoid embarrassment on the launch day.
If you're in US, try to use one of the high-end Amazon EC2's boxes as a dedicated server on launch day. Don't buy many of them, just 1, don't code scalability, don't be trapped in proprietary APIs, just rent a medium-to-high-end EC2 box for launch day. It's peanuts to have it for 24 hours, just use it as your launch-day dedicated server. You can see afterwards what happens with the traffic and adapt.
Having said that, be careful with configuration and stuff like that. Most of the bottle-necks are with limits set too low or too high (too few MySQL connections, too many Apache workers that swap the box to the death and so on). If you tweak them right, 90% of the preparation is done.
Be proactive, be available, logged in, monitor the service latency's periodically on launch day and good luck!
The instance types are at http://aws.amazon.com/ec2/instance-types/ (you probably want Medium or Large)
The hourly prices are at http://aws.amazon.com/ec2/pricing/ (you want the "On-Demand" section)