IMHO you are thinking along the right lines.
Your key measurements aren't going to change and you will be as comfortably fit to the bike as possible from the get go.
I did something similar and when I continued to lose weight and my flexibility improved my riding posture changed on my road bike. There was no impact on my hybrid.
At which point the bars were lowered and the stem switched to accommodate a more aggressive riding posture.
From a purely practical perspective, there is never a perfect time, so don't say no to Santa.
