Stolen = Yes

If buy from Tiffany = Min 10k for a diamond with the smallest size. Usually around 12~15k.

No idea.

At least 9k if you opt for 0.18 which is their smallest size diamond.

That one also if got stock

If you think it's worth it, just bite the bullet and buy.

It's a once in a life thing.

Some people might say its branding or etc ( Since you can get cheaper outside with another brand ).

Your budget is 10k or 3k? Huge difference le.

Think through properly first la, do you wanna get into a marriage filled with debts & then stress at the end of each month or is marriage something that's supposed to be happy? I know of someone who got married & rack up a debt just to show off (please the wife), now can't even afford to go out yumcha with friends. Everyday sit at home & TV all the way. Mainly because it usually doesn't stop at the marriage. After wedding, then based on the same attitude, have to get "glamour" cars, house etc. Which practically doom you into eternal debt unless you strike toto 1 day.

Brand important or not?

If brand is important then naturally have to make do with lower specs. You're paying extra for the brand ma.

5th C - Certification. Get a diamond with GIA. Brand actually not important at least for me.

Tiffany diamond "allegedly" higher standards than GIA

They do waste a lot of the diamond by cutting it deeper than others would do.

Anyways, brands like Tiffany / Cartier / Van Cleef and Arpels don't need GIA cert. Their names alone command a respectable resale value, if you want to let go of them someday.