Sounds reasonable. Pay is 1.5x your salary and you're expecting to like the job (which is important). Additional monetary rewards are minimal at QP though. Their raise this year was 7% max and inflation here was over 8%. For QR8,400 you will be renting an average flat, unless you want to dip into your savings for a villa.

Singapore is a direct flight from Doha and you get 37 working days holiday/yr +2 one week Eid breaks. Plenty of time to go home for vacation if you're homesick.

It sounds like you would be leaving a secure job to come here though, which may be a risk. QP and Qatar aren't for everybody and I know quite a few people who returned home after 3 months for various reasons.