Hey yall, flying to VIDP/DEL in July and had some questions regarding the trip.

1) I am currently on Tmobile One plan that includes free international low speed data and msg. Any experience with the data quality? Will it be enough for using Whatsapp, uber, email?
2) I plan to grab a local sim card, however currently own an esim iPhone. Can I grab a sim card from the airport, if so which providers and what do they need? I will be traveling with some NRIs what do they need as well?
3) Im not an app power user, but have heard from friends that having access to particular apps before landing is beneficial to avail of service such as uber/taxi, whatsapp/basicallyeverything, paytm/tap and go services, rail app/booking tickets. Any lists would be greatly helpful. I would be a using non indian CC to pay will I have any issues using said apps?
4) Both inbound and outbound, booked on the same ticket, will have me transiting from the international to the domestic terminal, how does that work? Will i have to first deplane, clear customs, pick up baggage, talk to the transfer desk, recheck, perform domestic security check?
5) I wanted to spend some time at the holiday in express in terminal, anyone experiences of what to expect, and how the process works, and do i have to prebook?