You are an extremely worried dad. I think you really should be looking elsewhere too. Not just in Singapore. I have few friends there and I can't tell you how much they complain about not having enough Pakistanis there. I can see that as a problem since I was in small town with very few too no Pakistanis. How did I find a good guy then?? Well first I truly believed I will meet someone when its meant to be. So guess what, I went to Pakistan for a wedding.. my husband's parents were there, saw me, 3 months, I was married. So really you need to look at other places too. My husband was living here at that time in a different city.
If a guy wants to study and get good education, I'll think that as a positive thing. Of course he is ambitious and wants to get the best. If things happen, its good for your own daughter. Who doesn't want a good educated spouse??
I come from a family where we aren't allowed to date at all. Period. I was friends in the university with guys... that's it. No dating nothing.
What did work for my sister though (her's wasn't an arranged marriage) was my parents inviting the guy over for dinner. My BIL spent a lot of time with my family, had dinners, lunches with us as a family before he got married to my sister. We have this bond with him.. the whole family does that is just amazing. He is like a brother to us.
You shouldn't judge the guy's intentions unless you are truly and honestly interested in him and so is your daughter.. Lets say you daughter isn't, you shouldn't consider him at all and no judging of course. But if you do get a hint kuch ho sakhta hai, then you should invite him more often and see how he gets along with your daughter. Talking on the phone is totally different. Maybe your son can befriend him and you can get to know more about him from your son.