The current limits are that you can save two links, one template and paste a schedule up to three days into the future.
When you paste your availability into a draft email and when you create a draft meeting invite using SpeedyG, it will include the text "SpeedyG assisted" hyperlinked to the SpeedyG website. This can be turned off in the Pro plan.
Yes, you can add as many users as you like at the "Pro" price.
No. SpeedyG is a month to month subscription.