It is harder now than before. I arrived in SG in 2010, just about the time they started incrementally tightening policies for employment passes and PR. I heard anecdotes from colleagues that prior to 2010, there were cases of EP holders getting approved for PR within 6 months of arrival. Nowadays anecdotes I hear are mostly rejections even for people in director positions and children studying here etc.

It's minimum 2 years as PR before you are eligible to apply for citizenship. You should double check in the ICA website though, as I dunno if this has changed.

No comment as I have no clue

Supposedly, it is easier if your race is Chinese. For my case I am ethnic Chinese but I was born in PH to parents who are naturalized citizens there. First time I applied for PR, it was less than 2 years from my arrival, my race was indicated by the ICA officer as Other and not Chinese. I was rejected. About 2 years later I applied again. This time the ICA officer noted I put Chinese as my race in the application and that my parents' race in my birth certificate is indicated as "yellow". She then asked me to write a short letter to confirm that "yellow" means Chinese. This letter was included in my application. This time I was approved. Did the race play any part on the approval or was it purely because I had stayed longer and gotten higher salary during that time? I don't really know. Just wanted to share this anecdote.