this one depends on your partner as well as her circle of friends which indirectly sets her expectation... so if all her married friends is wearing 1 carat... then 1 carat ring is normal..

having said that, buy within your means... if 0.3 is what you can afford then go for it... if she gets upset it's small then maybe you shouldn't marry her lol

reputable shops like those commercial ones SK, poh kong etc....

Diamonds they will explain the 4C bla bla bla... cut, clarity, color, etc.... the lowest priority should be color because naked eye can't really tell the difference.... the cut of the diamond is most important... if it's cut well it'll be shiny so that's something eye can tell difference

good luck bro and congrats!

oh 1 more thing... SK got lab grown diamonds which is the same as actual diamonds except it's lab grown, they call it Star Carat or something

with your budget, get lab grown one can get a bigger carat... but of course make sure she's okay with it la...