Hi,
For #1 - there is a link http://t.co/meeting which will help you setup that appointment.
For #2 - we don’t allow for multiple app IDs and you have to do testing with the same app. We usually recommend to setup test ad accounts (sometimes needing to get approval from a Twitter sales rep to help set it up) and Twitter handles (most burden being having to associate phone number). As far as I know, 3 legged auth for onboarding users to your Ads API solution should not require redirect URL, please clarify the scenario if you definitely think you need to leverage it.
Thanks,
John