What cc best to enjoy flight booking and travel perks like lounge access or complimentary insurance?

Lounge - I use mostly combination of CITI PM, DBS ALT and x card

You don't need to charge the purchase to your card to enjoy lounge access. Lounge access is usually provided via Priority Pass, and not the credit card spend.

To answer your question, I don't think so, but it's better to cancel the card after 6 months/1 year, just to ensure they don't claw back the sign up bonus (if any). Do check up on their promotion T&C to confirm on that. Make sure all bills are paid as well.

For what card, if you are planning SQ, I recommend OCBC 90N (I have it too) as you get to earn 4 mpd till Feb 2020. That's pretty good considering it's local spending!

Amex is the best card for well to do travellers. They are designed for travellers and luxury shoppers.

If you can afford it, apply for the best card you have, and when your spending goes up, they will send you an invitation-only card.

It comes with great perks like business class flights at great discounts, fanciful hotels at a great rates.

My only grip is Amex does not waive card membership fees.

Another card worth noting is Citibank Premiermiles card. The miles earned never expire.