1. For Chat it may be better to consider the Jot Messenger since it might work better for one-on-one chats, typical for a dating site. Otherwise, yes, core apps and Paid Levels with Payments should get you covered. 

2. Events, Discussions and Timeline are all core apps and can be activated and deactivated with a single switch via UNA Studio. 

3. Server resoirces mostly depend on number of active users, not so much number of total registrations. With 30k members you might have around 20-30 online users at a time at best. A Cloud8 (https://una.io/page/hosting) or equivalent server should handle that easily.