So will that get me upgrades in future and there is no expiry as long as you add points how frequently?
As Cove mentioned, KF miles expire 3 years after they are earned (ie 3 years after you transfer from Citi in this case), but they can be extended once only for 6 months at a cost (paid with points). Also, bear in mind that if you plan to book award tickets, they just have to be ticketed before the miles expire, you don't have to fly before the expiry date. All things considered, this means miles earned now could in theory be used for flights over 4 years from now.
There is no expiry with Citi Rewards points though, so another option is to leave the points there until you need to use them, but that could have its own risks - ie Citi continuously changing the rules without necessarily telling anyone about it. There is some concern that at some stage Citi will devalue the conversion rate to KF miles, although it hasn't happened
yet for Signature or Select. For this reason some AFFers are now transferring Citi rewards points to KF on a monthly basis.
Do bigger points balance get a different colour card?
No. You only move up the tiers by earning "elite miles" - equivalent to QF status credits - which you can only do by flying. And you won't earn any elite miles on award tickets. You will earn elite miles for the original booked fare if you buy a Y ticket and use miles to upgrade. However, it will take a lot of Y flights to get Gold status with SQ, and silver is hardly worth bothering with. Hence people looking for Star Alliance status tend to credit to other programs such as TK, as mentioned by Pete above. But if your plan is to amass as many KF miles as possible and travel in J or F, you don't need status! IMHO status is really only useful when flying in Y.
EDIT: PS, if you are looking for status, SQ Gold does have a significant advantage over Gold with other Star Alliance programs - SQ gold get lounge access etc when flying domestically with VA.
