For a late January trip, I'm planning on booking two separate round-trip tickets for SEA-SIN and for SIN-TRZ.

1: Assuming I'm arriving at SIN with one 23Kgs baggage, what can I expect to pay (or not-pay) for the SIN-TRZ segment on Indigo, Air India Express, Scoot or Sri Lankan? Indigo says something like 15Kgs, but their description is not clear to me.

2: Can someone please share their recent self-transfer experience in SIN while flying to India? How much time should I allow between arrival and departure at SIN for a risk-free transfer?

3 - Some of the flights I'm looking at arrive late night at SIN (Asiana and Korean for example), leaving about 8+ hours before the next flight to India. What are the options to manage time at night at the airport? I have access to Priority Pass lounges.

I did this self transfer in Singapore once before, September-October 2017; but I was travelling with a very small check-in luggage, so it wasn't a concern at all. At that time, I arrived in SIN on UA1 at around 6:15AM and caught the Sri Lankan to CMB after collecting the bags and checking in again for 9:00ish departure. I remember the process being very smooth and well defined at SIN airport. I don't have much memory other than the airport being well worth the hype.

The reason I choose Singapore is because TRZ is better connected to Singapore (and Kuala Lumpur) than it is with any of the Indian airports.

Thank you for any advice/tips/DOs/Don'ts you can share.