I have the following types of sponsorships for a conference I'm organizing: Bronze, Silver, Gold, Platinum and need a package bigger than Platinum.

Congratulations on the launch of your Beta testing! That is half the battle. My advice would be to slowly do another round of Beta testing and inviting people who you know will give you good feedback and help you improve your app. Then in the mean time get PR to pump up your app again for launch in a month. Not every app when it launches is perfect, we all have to update apps on our phone constantly so do not be afraid to go live. If you would like to set up a phone call I would love to chat more in depth because I have two friends who have get apps that I may be able to connect you with who have been in the same shoes as you!

I think that Eventbrite is your best solution. It's simple to use from an organizer and user perspective, and there's little fuss in taking payments. No reason to get fancier.

When you say "2 platform app" are you referring to a multi-sided platform? or specifically a 2 sided marketplace? Like Uber that has a driver and a passenger? If this is the case I recommend you reading about multisided platforms — https://www.amazon.com.br/Matchmakers-New-Economics-Multisided-Platforms/dp/1633691721. Once you read it I will be glad to talk with you with this VIP link https://clarity.fm/mgalli/crack806-multisided but keep in mind I am not an expert, just a leaner too that can offer some little help.

Social Marketing - I know it goes without saying that social marketing will be talked about. But I think its important to stress what exactly they should be doing with it. So many people think social marketing means having a facebook page, a twitter page or pinterest and have no idea how to actually use these services to grow their brand and build a community around their product.

Try an infographic but if budget/skillset doesn't allow use a word doc and create a pdf. Whatever you do keep it short and sweet and a better suggestion is to use the body of an email for the actual pitch and the attachment/one pager or close too with supplemental info. No one likes reading and this is just an opener so they get a feel - you can answer detailed questions in a call/meeting