Have you thought about staying outside of the airport? While the Holiday Inn in T3 is convenient, there are plenty of other options in nearby Aerocity. I know that the Lemon Tree offers half-day rates. not sure if that would apply in your situation though. The JW Marriott had some seriously cheap rates a few weeks ago (~ $50 USD per night).

Regarding Wifi, I was in DEL about 4 weeks ago, the public wifi is pretty good. I don't remember the exact speeds, but it was good enough for basic web browsing and emails. The speeds in the Plaza Premium lounge however was pretty crappy. The location and thick walls make it difficult to get a good signal. But out in the gate area, the signals are better.

On the way back, I'd be nervous with a 95 min connection. They start boarding the EWR flight about 50-60 mins prior due to the extra security checks.

Make sure you know the latest rules regarding Air Suvidha, Covid testing, state specific passes, and PCR testing. The rules are constantly changing, and the Babus at the airport are unforgiving.