Matt,
Both hands are limited?
I would not recommend a 50 lb load on your first walk unless you have experience. You may have survived the walk, but is it repeatable, without injury? What distance did you cover in the hour?
Rucking will 2-3x per week will build an aerobic base as Lydiard discussed. You need a load that will keep your HR at about 65% - so you can conversate, but it is not easy to ... you need air every other word or so ... don't go glycolytic on your walks, save for short bouts of steep terrain.
Also, it will most effectively improve your posture if you posture properly under the load ... keep your hips under your head, don't let the pack bend you forward. Use your abs to hold it up ... keep your midline in front somewhat closed - not hollow, but not open either.
Keep your shoulders back and down - let the pack help you do this. It should feel like you are teetering between falling backward and remaining upright ... grades will change this obviously. When your upper back gets angry with you, elbows to the sky, fingers interlaced, for a few moments ... hands toward the sky for a few moments, fingers interlaced ... then adduct arms to the side, small circles, then to the rear, then down again - you'll thank me for that bit
Take small frequent steps ... do not step out to the front to speed up ... step faster to speed up. "Slight" heel to toe. Do not run ... use other forms of training to get an anaerobic power effect when your hands heal. Arm carriage to the rear will speed you up.
Packing the ruck is important ... keep the load close to you and about midback or higher. Use "filler" to lift up the KB in the pack. If this was your first time, I'd expect strap soreness. But make sure you have good equipment to minimize unnecessary fatigue.
I can't say enough good stuff about rucking ... take care of your feet!
Al