Not that advisable on this.

As the exchange rate will not be the same everyday, some banks also have slightly different rate. So if you were to work in SG for long term, better get a card there, simple. If short term, then you have to pay extra slightly sometimes.
Like last time I work 1 year contract in Qatar(now permanent already), the exchange rate could be different by almost rm0.10 for each Riyal I spend. But that time AMEX still got 5% cash back for every rm1 I spend on all categories, so no problem on this.
But for now left with dining cash back, will it really worth? I doubt so.

Check back your statement due date.
If you over that date, it will automatically charge late payment penalty and interest.
You have to pay before the due date to avoid this.

Visa Signature's TP can redeem hard cash while others cannot, so it should not be combining, something wrong on this I guess

Offer letter means nothing basically, letter of confirmation of service may have some evidence that you are employed, but different company, different duration. In other words, payslip are better.

Old days you sure can use such documents to apply, but now degree holder's quality are same as SPM holders last time.
Last week I went to see a house that cost rm800k, the agent on the spot ask what field I'm in, when I tell her from O&G, she can directly tells me which bank willing to do my business, CIMB, BSN, BI on the spot reject without seeing any documents, PBB, MBB need to see first. I tell her now to tell the banks I'm a half Qatari and working in Qatar and more banks opening up the door to see my documents first before approving
Nowadays banks are on defensive mode on approving loan and cards

Actually is almost all industries are affected, just that O&G are the worst hit.