Well you know facebook is just a snapshot of life, and certainly is not the whole story. Not many people document the night feeds when they didn't know whether they were coming or going they were so tired, or explosive diapers, sick down their best clothes - floor walking with colic, toddler tantrums - etc, etc.
I love my son, but am the first to admit it is not always easy being a parent, it's the steepest learning curve I ever had (and I'm not even mentioning the teenage years but believe me they are challenging). And that is co-parenting with a dependable loving partner - can't imagine it without him.
As for 'mini me', IMO forget that - they are mini themselves, just as we once were too, if you expect a mini version of yourself you will likely be disappointed. They will soon grow and make their own minds up about things, it's amazing how limited parental influence is too once they are among their peer group.
That said, maybe one day this will happen for you, but you are right to wait to be in the right place in life before you consider parenthood - be proud you have that sense.
In the meantime, if your sister does have kids, you have the prospect of being an auntie which in my experience is a wonderful thing to be. You get to have all the fun without the hard work/worry.