But I also feel that if you only learn aiki and poor posture and bad movement from the beginning your aikido will surely suck.
Please bear in mind this is my PERSONAL opinion and not ANYBODY elses !
Well...for me that doesn't make sense...to my experience.
1. Virtually all of the people I have ever met in your art were taught through waza.
2. Every single one of them suffer from an array of structural flaws.
3. Every single one of them learned to fix them through Aiki and not waza.
4. Structural flaws are not standing up straight. You can have great structure and be fluid and dodging head strikes while bobbing and weaving. If you fight even a moderately skilled fighter while standing vertical...well...it won't last long.
Structure is a complicated thing. Having structure that will sustain itself by producing soft power in a formless state is a learned skill requiring much training.