I violate your requested 'data pool', so if your adamant about that don't read but it won't hurt you to.
I've been around long enough to see too many 'young people' get married too early, this may not be you, but to me tossing in 'her brother...' hints at that you might be feeling like you should because him/others etc.
I'm the kind of person that when I get married I want it to be forever, I don't want a second wife, so dating for several years like 3-5 if not more is mandatory before marriage and then I'm selfish so if kids are in the 'plan' another 3-5 years of just me and my wifey living it up.
That's me, only you can decide what's for you, if you really love this woman and are ready and want this then you can go for it now or a few months whatever. You can also make your engagement a year long or more, lots of people today get married in less than a year after proposing so it is almost like 'lets get married', mandatory wedding plans, ok time for the wedding. If your trying to figure out for yourself when the right time is, your kinda on your own, its all up to you. The only thing that might factor in that is if she is intent on getting married sooner rather than later or what, I'm sure after nearly 4 years you have talked a little bit about eachothers views on marriage so you have an idea about whether she will wait, if thats what you want to do, or if she's in a 'hurry'.
You can 'put this off' for as long as you want, but if she wants to get married sooner you may face losing her if you keep 'putting it off' it is complicated and up to you/her based on what you both want.